"That has to be it," Rick agreed. "Now, why try to lead us on like that? It was only an accident that Scotty and I didn't go in together, because his shoe needed tying. Otherwise, we'd both have been at the bottom of the quarry."

Dr. Miller shook his head, in bewilderment, not in negation. "You might very well have been hurt seriously or even killed. In which case people would have blamed the ghost. But why did the ghost do such a thing?"

Rick had wondered about this, too. "I can think of only one reason. The ghost can't stand investigation. He knew we were a menace because Scotty and I ran right up and tried to catch him that first night."

"But why did he tamper with your plane, or try to?" the scientist asked. "He couldn't have known about the alarm. You checked the plane, didn't you?"

"Yes. It wasn't touched, so far as we could see. Anyway, no harm was done. I can't imagine why he went for the plane, though, unless he figured on sabotaging us that way."

"You still haven't told us why you suspect the Frostola man," Barby pointed out.

Rick ticked off the points on his fingers. "He's new. He arrived just as the ghost started making appearances. But he's not so new that he hasn't had time to study the area or to make plans to lead nosy people to the quarry. He was at the picnic ground when there was no chance of selling much ice cream. He took the cement bags; we don't know why. He's tall and lean, so he could run fast enough to keep ahead of Scotty and me. He's also tall enough to qualify for the ghost we chased."

He stopped and took a deep breath. "And one more thing. He carries something that would make a marvelous mist for a ghost to appear in. Something that might harm the microscopic animals in the pool temporarily—although I'm not sure of this—but would be gone with the mist."

The others stared at him with complete interest.

Dr. Miller said softly, "Of course! Rick, that's brilliant. It fits perfectly!"

Jan Miller wailed, "What does?"

"Dry ice," Rick said.



CHAPTER IX

The Splitting Atoms

The storm had given way to a fine drizzle of rain by morning. Rick stared out the window at the drenched land and considered the angles he had been turning over in his mind.

The dry-ice theory wasn't conclusive, he knew, but it was a strong indication. It didn't explain the Blue Ghost himself, but it could explain the mist.

Dry ice is simply solid carbon dioxide, which is a gas at normal temperatures. It becomes a solid at low temperatures, and because it is harmless, inexpensive, and clean, it is widely used to keep things cold, as in the case of ice-cream route men who have no means of refrigeration.

When the temperature is raised, dry ice passes directly from the solid to the gaseous state. When dropped into water it seems to boil, as the comparative warmth of the water turns it to gas, and it creates a fine white mist.

Rick was reasonably sure the Blue Ghost appeared in a carbon-dioxide cloud, and he was beginning to have an inkling of how this was accomplished—in principle, if not in specific terms. There were, after all, he reasoned, only a few ways of creating a visible image. He was going through the list of possibilities, eliminating them one by one.

If the Frostola man was connected with the ghostly appearances, it was only necessary to keep track of that tall individual. This was Rick's plan, necessarily postponed because of the storm.

"Wish we had a radio," he said. "I'd like to get a weather report."

Scotty grinned sympathetically. He knew that Rick was impatient when there was detecting to be done.

"We really should have a battery radio," Dr. Miller said. "Power here is not very dependable in stormy weather. I think I'll get one, although that won't help now."

"What we need is a radio that doesn't depend on power," Jan Miller said. "Then it would always be ready."

Rick stared at the girl, not really seeing her. A radio without power. He remembered a long talk with Dr. John Gordon of the Spindrift staff about the principles of radio. Dr. Gordon had sketched a circuit that needed no power, and then had told Rick of how American ingenuity had produced what soldiers called a "foxhole radio."

"I saw an old transformer in the woodshed," he said suddenly. "May I have it, Dr. Miller?" At the scientist's nod, he addressed Jan. "I'll bet you can find me a cardboard tube. Then, if I can have an old razor blade and permission to take the receiver off the telephone for a while, I can make a radio!"

The scientist, the girls, and Scotty looked at him with disbelief. "He's gone off his rocker at last," Scotty muttered. "How can anyone make a radio out of junk?"

"I'll need a pencil stub, a few screws, and a piece of board," Rick added. "A safety pin would help, too."

"Rick Brant, you're being silly," Barby said firmly. "This is no time for practical jokes!"

Dr. Miller held up his hand. "Peace, Barbara. Rick isn't joking. I believe I see what he has in mind. Rick, I've never heard of this, but I assume the oxide on the razor blade is to act as a rectifier?"

"That's right, sir. John Gordon told me about it."

The scientist rose. "Then it will work. Come on, gang. Let's build a radio out of junk."

With many hands to help, the work went quickly. Under Dr. Miller's direction, Scotty took the transformer out of its case and the girls went to work unwinding the quantities of wire from its coils.

Rick found a razor blade and anchored it to a rectangular piece of plywood he found in the woodshed. It was a double-edged blade, and one small screw from Dr. Miller's junk box served to hold it. He wrapped a short piece of insulated wire, one of the transformer's connecting leads, under the screw before he tightened it. He sharpened the lead pencil with his jackknife, uncoiled the safety pin, and pushed the sharp end into the exposed lead at the upper end of the pencil, which was a stub only two inches long.

The safety pin also was screwed to the board, the screw going through the space in the pin's head. It was placed in such a position that the sharp end of the lead pencil rested on the razor blade. Another short piece of insulated wire was wrapped around the screw before it was tightened. Rick bared the copper end of the wire in order to make a good contact.

Jan found a cardboard roll that had once held paper towels. Rick cut off about six inches of it and proceeded to wind it with wire from the transformer. He wound evenly and tightly, until the roll was full of wire. Then he stabbed a small hole in each end of the roll and pulled the wires through to hold the coil in position. The roll—now a coil—was tacked to the board with thumbtacks.

Dr. Miller, meanwhile, had taken the receiver from the telephone. Scotty strung yards of wire around the room and handed the loose end to Rick. That was the antenna. Then Scotty scraped a bright place on a water pipe with his knife and twisted a length of wire tightly around it. That was the ground.

Rick and Dr. Miller made connections. Rick gestured to the haywire apparatus with some pride. "Behold. Where there was junk is now a radio."

Jan Miller said, "I don't believe it!"

Rick had to laugh. "I'm not sure I do, either. But let's try." He sat down at the table and held the receiver to his ear. With the other hand he began the laborious job of locating a sensitive spot on the razor blade.

Dr. Gordon had told him that only an occasional spot on a blade will work. Some blades have no such spots. Others have many.

Rick was beginning to think that he had one of the no-spot kind, or that the whole idea was wrong, when he heard what he thought was a voice. He hastily concentrated on the spot, and in a few seconds music flooded into the earphone. He had caught a disk jockey in the process of introducing a record. For a long moment he listened, then held out the earphone with a broad grin. "Anyone care to listen?"

Everyone did. They took turns, with each application of the phone to an ear accompanied by expressions of astonishment.

Barby looked at her brother with new respect. "It's just fantastic! How on earth does it work?"

Dr. Miller chuckled. "I'm sure you don't want a full course in electronics, Barby. Actually, it's simple enough. The signal from the radio station is an alternating current that sets up a corresponding current in the antenna wire. This current goes through the coil and is rectified—that is, it's turned into pulsating direct current—by the razor blade. The receiver then converts it into audible sound."

Barby sighed. "I'll just have to take your word for it. But it's a miracle!"

"It may seem like one, but it's really the same kind of circuit you find in a crystal set," Rick explained. "The razor blade acts like the crystal. That's all."

The young people took turns listening to the station, located in a town nearby. Within the hour there was a weather report promising clearing skies before the end of the day. Later, in a roundup of local announcements, they heard that the annual Sons of the Old Dominion feast, postponed because of the storm, would be held the next night.

"That means we start keeping an eye on the ice-cream man tomorrow afternoon," Rick said.

Scotty nodded. "First, we'd better make a survey of the terrain. He has to approach by the road, but there are a million places he could go once he got into the mine area."

Rick looked out the window. "The rain has stopped. Maybe we can reconnoiter this afternoon."

Fortunately, the Miller farm was well equipped with boots and overshoes. The boys borrowed footgear suitable for any mud left by the rain and started out after lunch.

The picnic area was washed clean of footprints and it was clear no one had visited the area since the rain. They made their way to the top of the hill above the mine and surveyed the cornfield that had been planted on the hilltop field. The corn was not high. The plants came only to their knees. Either it was a second planting or a poor crop. Rick guessed that the second reason was probably the correct one, because the field hadn't been cultivated recently.

"This isn't Miller land," he mused. "Wonder who is farming it?"

"It must be Hilleboe's property," Scotty returned. "Maybe he rents it to some local farmer."

They walked to the downstream edge of the cornfield to where the woods resumed. Rick had a feeling that they were wasting time. The ghost couldn't be produced from such a distance by any means he had ever heard of. The apparition had to be created right in the vicinity of the mine.

He spoke his thoughts aloud, and added, "Let's go back."

"Just a minute." Scotty pointed to a pile of brush. "Aren't those more bags?"

They were, and of the same brand as those the boys had located on the stream bank. Scotty picked one up and tested it between his fingers. "Mighty curious. Water cures Portland cement. Turns it hard. These bags aren't hard, even though some powder is still in them."

Rick examined the bags, his brows creased with bewilderment. "They must have held something besides cement. But what? Fertilizer for the cornfield, maybe? And why two caches?"

"If it were fertilizer, the bags near the mine could have been for the field across the creek where the plane is," Scotty suggested. "These could have been for this field. But I don't think it was fertilizer. Isn't fertilizer soluble in water?"

Rick wasn't sure. "We can take the bag along," he said. "Maybe the microscope will tell us something, or maybe Dr. Miller will know."

He had a feeling that the bags meant something. They had been hidden, and only the erosion of rain had uncovered them, first at the creek embankment and now here. The Frostola man had almost certainly taken the others. Why? Unless they had something to do with the mystery? The bags were worthless, of themselves.

They finished the survey of the area. It was clear that whoever produced the ghost would have to enter by the road from town, because there was no other road on the side of the hill in which the mine was located. To be sure, the area could be reached by walking a considerable distance, but Rick couldn't see a man with equipment doing much walking through cornfields or woods filled with underbrush. He was certain the ghost had to be produced by equipment of some kind, probably electric powered—which meant batteries.

The problem was, where did the ghost producer operate? If dry ice was used to produce the mist, how did it get into the pool? He had no answers to these vital questions, nor did Scotty.

The dark-haired boy looked at him quizzically as they trudged back to the farmhouse. "Did it ever occur to you that it's impossible for anyone to produce the ghost? There is no place within sight of the pool where anyone could hide, except in a tree, and a man with equipment wouldn't go undetected by a gang at the picnic grounds."

"It did occur to me," Rick admitted. "But doesn't that put us back where we started? Either the ghost is a genuine spook, or it's man-made. We're not making many miles an hour in proving it's man-made, I admit. But if it isn't, where does that leave us?"

Rick remembered the chase through the woods, ending with a bath in the quarry. If they had been chasing a real ghost, and the ghost had led them into danger deliberately, that meant ... He wasn't sure what it meant except that it gave him goose pimples to think about it.

The electricity and telephone service had been restored by the time the boys got back. Dr. Miller told them that he had phoned the tenant farmer and arranged for the man to do a little inquiring in the town.

Rick displayed the bag. "Got a specimen," he told the group. He explained their interest in the bag and asked Dr. Miller if he could identify the contents.

The scientist examined the grayish powder from the bag. "It could be any one of a hundred things," he said. "Let's see what we can find out about it."

The farmhouse wasn't equipped for any kind of chemical analysis, but the scientist did what was possible. He tried to dissolve the powder in water, and failed. He tried vinegar, as the only acid available, and failed. He tried ammonia, and failed.

Finally he said, "Well, it isn't cement, and it isn't fertilizer. It's an inorganic substance. I suggest the microscope, Rick. It will at least give us a clue to its structure, if not its identity."

Rick spread a small amount on a slide, switched on the substage light, and put the slide on the stage. He focused, using his highest-power lens combination which gave a magnification of three hundred times.

The powder was clearly crystalline, a mineral of some kind. Rick couldn't identify it. He turned the eyepiece over to Dr. Miller. The scientist had no better luck.

Barby asked, "Could it be an explosive?"

"No, Barby. This is powdered rock of some kind," Dr. Miller answered, his eye at the instrument. "But why anyone should use powdered rock and then hide the bags certainly escapes me. I can't imagine what the powder is for. It isn't a powdered limestone, which might be used on the fields. The crystal structure is wrong for that."

"Wish we had a geologist with us," Rick said. "This calls for an expert." He stared helplessly at the microscope. There was only one more test that could be made, and he saw no use in making it.



Included in the microscopy set Barby had given him was a gadget called a spinthariscope, like a cone of black plastic with the sharp end of the cone sliced off. In the wide end of the cone, inset so it wouldn't touch the eye, was a lens. The small end was composed of a disk of special chemical that fluoresced when struck by an atomic particle.

The little instrument used a principle dating back to the early history of atomic energy, when scientists were exploring the nature of the strange force the Curies had discovered in radium and polonium.

It was only his training in thoroughness of investigation that led Rick to use the instrument. Since it was necessary for the eye to become adapted to the darkness before using the instrument, he took it into a closet and shut the door. As the pupils of his eyes dilated he worked by touch, spreading a bit of powder on the end containing the special sulfide screen.

He applied his eye to the lens, more as a matter of form than in the expectation of seeing anything. For an instant he saw nothing, then, as his eye adjusted, he let out a wild yell. There were hundreds of scintillations, each caused by a nuclear particle or photon striking the screen.

The sample was radioactive!



CHAPTER X

An Assist from JANIG

"We're onto something," Rick said grimly, "and we need help."

"I should say so," Barby commented. She eyed the cement bag a little apprehensively. "After all, radioactivity is dangerous!"

Dr. Miller smiled. "It is, in sufficient quantity. But the sample we have here is scarcely above normal background, so I don't think we need be concerned." The scientist turned to Rick. "I wish your instrument could give us further data, but unfortunately it's pretty primitive. It tells us the sample is slightly radioactive and that's all. I agree we need help."

The nearest source of help Rick could think of was JANIG, the secret security agency in Washington for which the Spindrift scientists had often worked on special projects. This wasn't a matter for the agency officially, but Rick was sure Steve Ames, their contact in JANIG, would help if he could. Since Spindrift had first worked with the agency on The Whispering Box Mystery, Steve and the boys had become good friends.

Rick suggested to the others that Steve should be called. All of them knew the young agent. He had been responsible to a large extent for the Millers joining the Spindrift staff, since he had smuggled them out of Washington to Spindrift to escape the deadly electronic mind reader that had imperiled the scientist for weeks.

There was no disagreement. On the contrary, Jan Miller asked excitedly, "What's the matter with right now?"

"Nothing," Rick said with a grin. He went to the telephone book and found the long-range dialing code for Washington, then dialed Steve's special number directly. In less than half a minute he had the agent on the phone.

"Steve? What a break to find you in! This is Rick." He swiftly outlined the events of the past few days, ending with the discovery that the bag contents were radioactive. He concluded, "I know this isn't a case for you, but we hoped you might help us to identify the stuff from the bag and get a better measure of how active it is."

Steve considered. "Know where Falls Church airport is?"

Rick had used it for a landmark on the way to the farm. It was a small private airport west of Washington near the city of Falls Church. "I know where it is."

"All right. You're only a few minutes flying time from there. It's now two thirty. Be there at four. I'll have a man meet you. Bring the sample."

Rick thanked the agent and hung up. He reported that Steve would send a man to the airport at four o'clock.

Scotty asked, "Is the field dry enough for take-off and landing?"

"Sure. I hope Steve has a real expert he can send. If we can identify this stuff, it may give us a clue to what's going on here."

At Barby's request, Rick and Scotty took the girls along for the short ride. Steve's man walked to the plane as they rolled to a stop on the Falls Church strip. He introduced himself as Don Baxter, then opened the suitcase he carried. "Let's see what you have."

He produced a field-survey instrument and held it over the bag Rick carried. The instrument's meter showed a reading at once.

"Gamma," Baxter stated. "Now let's try for alpha and beta." He opened a shield on the bottom of his instrument and checked the sample again. The meter failed to respond. "No beta. That's interesting." An inner shield was slid out of the way and the instrument held to the bag. The meter responded.

Baxter nodded satisfaction. "Alpha and gamma. No beta. That means this stuff is not a fission product."

He studied the powder and rubbed a bit between his thumb and forefinger. He asked, "May I have the bag?"

"Sure," Rick agreed readily. "What is the stuff?"

Baxter took the cement bag and folded it neatly, then he took a plastic bag from his case and put the cement bag inside. "I can't be sure," he said. "About its precise identity, I mean. But it seems to be pulverized ore, and my guess would be carnotite. Don't worry about the radioactivity. You could live in a house made of this stuff and it wouldn't be dangerous. The level of activity is very low. I suppose you have no idea where the sample came from?"

Rick shook his head. "Where does carnotite come from, usually?"

"The Colorado Plateau, for the most part. There are other deposits, but none around here. This stuff was almost certainly imported. Have you any idea why?"

"Not the slightest. It's a complete mystery."

Baxter nodded. "Well, that's all I can do for now. I'll analyze the sample and let Steve Ames know exactly what it is, but I'm betting on carnotite. If you find a few hundred tons of it, you can sell it to the Atomic Energy Commission. So long."

The expert tipped his hat to the girls and walked to his car.

"What was that all about?" Barby demanded. "You and Scotty seemed to know what he was talking about, but it was all Greek to Jan and me."

Rick explained on the way back to the farm. "There are four main kinds of radioactivity. They're called alpha, beta, gamma, and neutrons. Our sample has alpha and gamma. That means it doesn't come from either bomb debris or from a reactor, because fission takes place in both, and there is almost always beta activity as well as gamma in the products of fission. But some isotopes of uranium and thorium have little beta, with some alpha and gamma, so Baxter concluded we had powdered uranium ore. There are many kinds of ore. Pitchblende is the best, but carnotite, which is a gray rock with yellowish streaks, is also good ore. Got it now?"

Jan Miller asked, "How do you know all this, Rick?"

The boy chuckled. "From associating with your father and mine, not to mention Weiss, Zircon, and the other scientists. They talk and Scotty and I listen. Also, Dad has a lot of books on atomic energy, and some of them are simple enough for me to read."

The Sky Wagon was over the Miller farm in a very short time, but before landing Rick made a swing of the area. The young people readily identified the mine and picnic grounds, and Rick pointed out the quarry into which he had tumbled.

Scotty said, "Something's been bothering me. If the Frostola man is new in this area, how could he have known the terrain well enough to lead us on that wild-goose chase?"

"He's new, but not that new," Rick pointed out. "He's had weeks in which to study the lay of the land. Besides, he does his haunting at night—if he's the one—and he roams the fields near the mine. He must know his way around."

"You're right," Scotty assented. "Now tell me this: why did he take the cement bags?"

"To keep us from finding out that they didn't contain cement," Rick said. "It has to be the reason. That means he knew about the bags, and maybe he even buried them. He didn't bury them deep, because who would think anything of a bunch of cement bags, except a pair like us? Then, when he saw they had turned up, he collected them and took them somewhere else. The bags we found this morning may even be the same ones, although I think they're a second set. He'd hide the first set better than he did at first."

"Your language is confused, but I get your meaning." Scotty grinned. "Okay, detective. Set us down. It's suppertime."

Rick swung into his landing pattern. "Anyway, we've made progress," he commented with satisfaction. "We started with just a ghost. Now look what we've got!"



CHAPTER XI

The Ghost Reappears

Belsely, the tenant farmer, had no difficulty in establishing a connection between Jethro Collins, real-estate agent, and the Frostola man. He made a quick trip to town on the morning following the flight to Falls Church, and reported that the ice-cream vendor was renting a room from Collins.

"No doubt about that connection," was Rick's comment. Then, because they had not talked to Belsely at any length, he questioned the farmer about the appearances of the ghost in the fields nearby.

"I've seen him four or five times, not counting the night you chased him," the farmer said. "Funny thing about the night he got the alarm going on your plane."

"What was funny?" Scotty asked.

"He was alone."

"But he's always alone," Rick exclaimed.

"Nope. He's alone at the mine, but when he walks the fields he has some of his men with him. Sometimes one, sometimes two or three. Only saw him alone that once—the night you chased him."

This was a new angle. Rick and Scotty looked at each other, puzzled.

"You've seen the others?" Scotty asked.

"Sure have. Not close to, you can bet. Got no wish to tangle with spirits, not me. But I saw them. They walked in the cornfield on top of the mine hill, and they walked in the field where your plane is. They was lookin' for somethin'."

"How do you know?" Rick demanded.

"They'd walk, then stop, and bend over. Like they were searchin' the ground. Bet one of 'em lost a head and is huntin' for it."

"Did you see where they came from, or went to?"

"Not me. I got curiosity, but not the kind that killed that cat they tell about. Like I say, me and spirits don't mix, none to speak of."

Rick pondered the information. "Are these ghostly walks at nine o'clock?"

"No. Mostly around midnight."

Rick turned to Scotty. "What do you make of that?"

"Nothing," Scotty replied. "Not a thing. You say you've seen as many as three men plus the Blue Ghost?"

"That's correct. None of them shine like the Blue Ghost himself, though. Most curious thing I ever saw was the night they pulled a wagon, collectin' the invisible dead from the battlefield."

Rick's hair had an impulse to stand on end. The calm, factual way in which the tenant farmer piled mystery on mystery was incredible.

"You mean you saw ghosts pulling a ghost wagon?" the boy asked incredulously.

"Like I said. More a cart than a wagon, I suppose you'd say. They hauled it back and forth, and the mist trailed out behind it. Once in a while they'd stop and gather and look at the ground. Must be they were searchin' for their dead. Don't know why else they'd need a wagon. And that Blue Thing leadin' the way every time. Up and down, back and forth."

Scotty asked, "Where were you while all this was going on?"

"In the orchard, scared pink, but not so scared as curious."

A man of real courage, Rick thought. Believed in ghosts, but had the nerve to watch them in action. "Mr. Belsely, you said none of them shone like the Blue Ghost. Did the others look solid?"

"They were dark shadows, that's all. No moon to see by, or at least not enough. Couldn't make out what they looked like."

"Has anyone else seen them in the fields?" Scotty wanted to know.

"Sure enough. Two or three that I know of, maybe more."

The tenant farmer paused, then asked a question of his own. "Why are you so interested in this new ice-cream man?"

Rick considered. "He interested us," he said finally. "He's not a Virginian. And he didn't seem to know much about the ghost."

Belsely's comment brought Rick's carefully built up assumptions tumbling down around his ears. "Oh, he knows about the ghost, all right. He saw it once that I know of, when he was sellin' ice cream to the girl campers." The farmer added, "I was standin' right next to him at the time."

Rick looked at Scotty helplessly. "Thank you, Mr. Belsely," he said unhappily. "You've certainly given us plenty to think about!"

The boys watched as the tenant farmer walked up the road to his own house, as solid and dependable as the very earth he walked on. There was no arguing with what he had seen, only with his interpretation of it. Clearly, Rick thought, he had seen figures in the fields on several occasions. But what had the figures actually been doing?

"Don't be too discouraged," Scotty offered. "The ice-cream man seeing the ghost doesn't mean he isn't involved. Wasn't the girls' picnic the first time the ghost made a public appearance? He may have been checking on the way the ghost looked."

"What do you suppose Belsely was doing there?" Rick asked.

"Probably just wandered over to see what was going on. I've noticed people are pretty casual about the affairs over there. No reason why Belsely wouldn't take an evening stroll to see how the party was going."

"Well keep our plan," Rick decided. "It's the only lead we have, so we'd better use it."

By the time the Sons of the Old Dominion started to arrive for the annual feast, the boys were in their chosen position, upstream from the mine at a point where they couldn't fail to see all who traveled the road, but where no one could see them through the thick screen of foliage.

They had applied insect repellent liberally, but the insects swarmed around them anyway, although bites were few. They lay quietly and watched car after car arrive, but without seeing a familiar face.

During a lull in the traffic Rick asked, "Do you suppose we got here too late? He may have come earlier."

"I doubt it. Besides, where would he have parked his scooter? It isn't anywhere between us and the mine because we looked, and I doubt that he'd walk any farther than this."

Rick had to agree that it wouldn't make much sense to park the vehicle any farther away than the spot they had selected from which to watch.

The traffic ceased. All Sons of the Old Dominion apparently had arrived, and all were presumably feasting on good food. It was only eight o'clock; the ghost wasn't due for an hour. Rick thought an hour was probably more than the ghost producer needed to get ready for his appearance. Only a few minutes might be needed. That meant he and Scotty would have to wait until a few minutes before nine, to be sure no one slipped by.

One late arrival roared past as they waited, and then all was quiet. At ten minutes to nine Rick admitted defeat. "Either he isn't coming, or he got there through the fields. Let's go see if he shows up."

As they hiked down the road, ears attuned for a motor vehicle behind them, Rick explained his theory of ghost production to Scotty. "There's only one way a transparent spook can be produced, and that's optically. In the movies they use a double exposure. The only way to produce an optical image on mist is with a projector of some kind."

"Spook projector," Scotty agreed. "Only where is this projector located?"

That, Rick pointed out, was the prize-winning question. "All we can do is keep an eye open for the projector beam."

"Both eyes," Scotty corrected.

It was one minute before nine when they arrived at the mine entrance. The Sons of the Old Dominion were still eating, but there was a lack of noise or joyousness that made Rick aware that the Sons knew about the ghost. He saw groups facing the place where the ghost would appear.

The boys were in front of the mine entrance. By unspoken agreement they moved to a position directly in front of the pool. If the ghost appeared, it would be almost over their heads. The shelf was too high for them to see into the water, but they were in a position where any human activity couldn't possibly be overlooked.

"On your toes," Scotty whispered. "Let's rush it while the Blue Ghost is still there."

Rick swallowed hard. In spite of his conviction that a human agency, and not a supernatural one, produced the Blue Ghost, he didn't care much for rushing right into the apparition. In fact, he didn't like it at all. The mist had felt clammy the first time, even though no harm had come to them. But, he told himself sternly, Scotty was right. They either had faith in their assumptions or they didn't.

"Wait until the show is almost over," Rick whispered.

A voice from behind them called, "Better get out of there, you two. That's where the ghost appears."

The boys turned to reassure their well-wisher, and in that moment a sigh went up from the crowd. Rick heard a sudden splash, and then the white mist was rising, billowing almost over their heads!

He watched, fascinated and scared, and saw the Blue Ghost appear. The apparition was elongated from Rick's viewpoint, but the act was the same. The boy saw no sign of a projector beam, no sign of any human agency, and the lack of both turned his knees to water. He was close—very close—yet he could detect no sign of human origin in the thing overhead. Horror swept through him. Had he been wrong, he and Scotty?

His pal's hand fell sharply on his back. "Let's get him, boy! Let's find out for once and all!"

Somehow he got his legs moving. He and Scotty went up the steep slope, scrambling right toward the thing that was now holding out bloody hands!

They were in the mist! Rick sensed the blueness around him, and with sick horror realized that the ghost continued his act as though they were not even there.

Scotty yelled, and in the same instant sharp pain swept across Rick's face. Bitter, terrible cold encompassed him, turned the skin on his face rigid, seared his eyeballs with cold so intense it was like burning heat. He staggered and fell, hands clutching his frozen face. He tried to yell for help and couldn't. He rolled down the hillside that he had climbed seconds before, and Scotty's falling body crashed into him, knocked the breath from him.

And overhead, the vision of the Union cavalry officer, face distorted in agony, faded slowly from sight, leaving only the icy, billowing mist.



CHAPTER XII

The Dead Water

Hands lifted Rick and Scotty to their feet and voices demanded to know what had happened. Other voices berated them, calling them a pair of young idiots for rushing a ghost like that.

Rick staggered in the grip of the supporting hands. His heart was pounding and there was a constriction in his chest. Tears streamed down his cheeks as his tear ducts spouted fluid to protect his eyes from the now-vanishing cold. His cheeks felt numb, but sensation was returning.

At last he regained his equilibrium and found his handkerchief. He mopped his face and suddenly realized that his face was flushed, as though with fever. The sensation of burning cold was gone. He took a deep breath, grateful to be nearly normal again.

Scotty was also back to near normal. To the questions from the surrounding circle of Sons of the Old Dominion they could only say that they didn't know what had happened.

"Suddenly our faces froze," Rick explained shakily. "At least mine did."

"Same here," Scotty supplemented.

"It was like the cold of ... of ... I don't know, really. It was cold, but like nothing I've ever experienced before. The shock was so great I just sort of crumpled and fell."

"Whatever made you rush right into the ghost like that?" a burly man wanted to know.

Rick shrugged. "We didn't think the ghost was real, and we wanted to see how it was produced."

"Do you believe it's real now?"

The boy shuddered. "I'm a whole lot closer to believing it," he admitted.

"At least we won't try football tactics on it again," Scotty added.

Seeing that the boys were all right, the group dispersed. In a few moments they were alone. Rick shook his head hard, to clear it. "Now where are we?" he asked.

Scotty laughed mirthlessly. "I'm glad you asked that. I'd be gladder if you could answer it."

"One thing more and I'm ready to call quits," Rick said. Common sense told him to beat a path to the Millers, but he was stubborn. He wasn't giving up yet. He searched until he found a coke bottle, then taking his nerve in both hands he climbed up to the pool. He let the bottle fill with spring water then rinsed it. When he was satisfied it was clean enough, he filled it from the pool—the same pool from which the ghostly mist had appeared only short minutes before.

Only then did he and Scotty leave the picnic grounds and proceed home to the Miller farmhouse.

The Millers and the girls were waiting. One look at the boys' faces and they knew something had happened.

Jan Miller said with quick intuition, "You're hurt!"

"Not permanently," Rick reassured her. "For a while we wondered, but it's okay now."

The Millers and the girls listened to their recital with mixed horror and relief that the effect of the cold had vanished so quickly. Dr. Miller's brows were knit as he tried to puzzle out what had happened.

"You saw no projection beam, I assume?"

"Not a trace," Rick said emphatically.

"You were actually in the mist when this cold effect hit you?" Dr. Miller asked.

"I was," Rick agreed. "How about you, Scotty?"

"Same. I was groping around trying to find something to get my hands on. I was actually in the pool of water. Rick was on the edge of it."

Dr. Miller considered. "Even if your assumption about dry ice is correct, Rick, that wouldn't explain the cold effect. If one touches dry ice, it is cold enough to cause a burning sensation, but had dry ice been used on you it would have taken chunks of it in contact with your skin. You felt nothing solid, I assume?"

Both boys shook their heads.

"Then we can rule out dry ice. I can't imagine what hit you."

"The Blue Ghost," Barby said, and shuddered visibly. "This ought to prove it, I guess."

Rick admitted it. "Ought to is right, but I'm stubborn enough to keep looking for a rational explanation. I got some water from the pool. Anyone want to look with me?"

They all did, and followed Rick to the kitchen. He set up the microscope and plugged in the substage light, then found a well slide and placed a drop of water on it. But examine the drop as he would, using the most powerful magnification, he could see nothing but a bit of brown debris that seemed to be a thread of withered alga.

He took another drop from the coke bottle and tried again with similar results. He shook the bottle and placed a third drop on a clean slide.

Rick focused the microscope on the drop of water. Yesterday—or was it the day before? He couldn't remember clearly he was so tired—the rock basin had been literally swarming with paramecia and other forms of life. Today, following the appearance of the ghost, the water from the basin was as devoid of life as the planet Jupiter.

He moved the well slide from side to side, bringing different parts of the drop under his lens. There was a tiny wisp of vegetable matter he recognized as a dead bit of Riccia, and a few black threads of algae.

Rick shook his head in bewilderment. "Whatever the Blue Ghost is," he stated, "it's a killer. The mob we saw is gone."

Dr. Miller took over the instrument and confirmed Rick's findings. "The water is dead," he said at last. "I don't know how useful it is to know that, but I can't imagine that a supernatural agency would bring death to millions of microscopic creatures. Yet, if it isn't supernatural, how is it done and who does it?"

"I've never seen such hard people to convince of anything," Barby declared. "All the evidence points to a real ghost, it seems to me. But you keep trying to prove something else and you don't get very far."

"We get as far as dead water and radioactive cement bags that don't contain cement," Rick pointed out. "For a while tonight I was about convinced that the ghost was supernatural, but I'm still going to be a doubting Thomas, at least until we run all leads into a dead end!"



CHAPTER XIII

The Night Watchers

Rick couldn't sleep. He kept trying for a comfortable position, but the hitherto excellent bed suddenly seemed full of lumps. His pillow wouldn't behave, either. It seemed determined to lump up and deprive him of sleep.

His body was tired enough, but his mind kept worrying the problem of the Blue Ghost endlessly, going over incidents and details, searching for a meaning, a clue that would lead to a conclusion.

What was the reason for the Blue Ghost? If he could only figure that much out the rest would follow naturally. If the assumption that the ghost was man-made was correct, there had to be some reason for the apparition.

So far as he knew, the ghost had had only one effect, and that was to reduce drastically the use of the picnic ground in front of the old mine. According to the Millers, the grounds were in constant use most years, with family parties, group affairs, and young people spending considerable time in swimming, eating, ball games, and all the other amusements of people who sought the coolness of trees and water to escape the Virginia summer heat.

Now use of the grounds was restricted to affairs of long standing that it would be inconvenient to change or to cancel.

That was a definite effect, he admitted to himself. But who could profit by it?

There was only one possible clue, and that lay in the midnight prowlings of the Blue Ghost and his varying number of companions. Turning the picnic area into a forbidding place, a haunted ground, would give the ghost and friends ample opportunity to roam the upper and lower fields without interference.

Only, why roam the fields?

Somehow, the radioactive dust in the cement bags must tie into it, but Rick couldn't imagine the connection. He thought of a secret uranium strike and rejected it. Empty bags pointed to something gotten rid of, not something gained by a discovery.

The thought was intriguing. If he assumed the bags had arrived full, what had happened to the contents? He tried to think of uses for the powdered ore and couldn't. Even if he could imagine a secret processing plant to extract the uranium for some purpose, there wasn't enough. A sufficient quantity of ore to provide even a gram of uranium metal would mean literally thousands of bags and they had found less than a dozen.

Of course there was the cart Belsely had seen. Rick couldn't credit the farmer's notion that the ghost soldiers had been collecting ghost bodies of the long-dead. But what had the cart been doing? The very idea of a cart led to the idea of something too heavy to be carried without mechanical aid. What? Bags of radioactive ore dust?

He was still tossing in his bed and chewing the data fine when the dogs began to bark. He listened. The barking was far away, probably a mile or more. There were farms on the road to town, and probably all of them had dogs.

Scotty spoke in a whisper. "What makes dogs bark at night?"

"Maybe a fox," Rick replied.

"Or a ghost?"

Rick sat bolt upright. "Maybe!"

Scotty swung to a sitting position on the side of his bed. "I've been listening to you twisting and turning for an hour. If you're going to keep me awake, it might as well be useful. What say we go look?"

Rick looked at the luminous dial of his watch. It was past midnight. "No chases ending in quarries?"

Scotty's chuckle was low. "No chases. Listen a minute!"

Rick held his breath, and heard what Scotty's keen ears had detected. There was the sound of a car somewhere far away. He couldn't tell the direction, but he was sure it was not the road from town because the bedroom windows opened on the town side of the farmhouse.

The night was clear and still, and sounds would carry great distances. The car might even be on the main highway, about five miles away.

"Let's get going," Rick said softly. He fumbled for his clothes on the chair at the foot of his bed and dressed quietly. Scotty was doing the same on his own side of the room.

They checked flashlights, then started down the stairs. The treads creaked noisily, as is the case in old houses, and Dr. Miller's voice stopped them.

"Going spook hunting?"

"Yes, sir," Rick replied softly. "We're going to see why the dogs are barking."

"No chases," the scientist warned. "If you should see anything, stay away from it. Watch from a respectful distance."

"We will," Rick promised.

Outside, the night was lighted only by stars and a crescent moon. Trees were dark shapes against the lighter darkness of the night as the boys made their way through the orchard. They headed for the plane, intending to stop at the edge of the orchard to reconnoiter.

The field before them stretched dark and empty to the trees along the creek, except for the angular bulk of the plane. Rick watched and listened with every sense alert. Insects hummed now and then, but that was all.

"Let's get to the tree belt," Scotty said in a whisper. "We can watch both fields from there."

"Okay." Rick led the way at a half trot that covered ground rapidly. In a few minutes they were across the creek and among the trees. They slowed their pace, stopping now and then to listen. The dogs were still barking, but the noise came from far away, on the other side of the hill in which the mine was located.

Scotty took the lead as they approached the picnic grounds. He was noiseless as a shadow, and Rick tried hard to step exactly in his footprints to avoid any noise.

Using the great oaks for cover, Scotty moved to the picnic grounds, among the tables and stone cooking pits. Suddenly he took Rick's arm and squeezed. Rick stopped instantly, ready for whatever action was indicated.

Scotty put his lips to Rick's ear. "Look around the tree, on top of the mine in the upland cornfield. Be very careful."

Rick moved into position, then with extreme caution he peered around the protecting tree. The first thing he saw on the hill was the Blue Ghost, not in his apparition form, but as the human-headed light they had chased. Then he realized that he was also seeing a form under the light, a human shape silhouetted faintly against the dark sky!

He choked back an exclamation. There were two other shapes, unlighted, but clearly human. This was what the tenant farmer had seen! But what were they doing in the cornfield? In a moment it became clear. The three were coming his way!

Scotty squeezed his shoulder and pointed up. Rick realized suddenly that they were hiding behind the oak in which they had watched unsuccessfully for the Blue Ghost. He jumped for the lowest branch and quickly hauled himself into the protecting foliage. Scotty was close behind him.

Through openings in the foliage they saw the Blue Ghost make his way down the hillside with his two companions, saw the three pause at the basin in which the ghost made his public appearances. Rick shuddered as he heard soft, ghostly laughter. He was convinced that he watched three men, but the memory of the bitter, burning cold on his face was still too fresh and green not to feel a reaction.

The ghostly trio continued down the slope to the picnic grounds and turned to the road that led to the bridge. Rick would have given much for enough moonlight to see details, but he could see only the three vague shapes. He thought the figure with the softly lighted apparatus on his head carried something in one hand, but he wasn't sure.

Not until the trio passed out of sight behind the trees did the boys descend from the tree, then they paused for a whispered consultation that couldn't have been heard three feet away.

"They must be heading for the field where the plane is parked," Rick guessed. "We want to keep an eye on them."

"That we will," Scotty assured him. "Follow me, old son. We're making real progress tonight!"

Scotty led the way through the tree belt to the bank of the creek. He paused in the trees long enough to be sure the ghost trio had crossed the creek, then picked positions behind the earthworks erected by Confederate soldiers long ago.

Rick watched the ghosts—for he thought of them by that useful term even though he now knew they were mortal—as they walked slowly across the field. He saw them pause, and saw the dark figures shorten as they bent over. He took a bearing on the spot, using the dim shape of his plane for one reference and the bridge for another. He thought he could locate the position again by daylight.

In a moment the three moved on again, while Rick watched, puzzled. He felt Scotty move and put his head close to hear what his pal had to say. "They had to come from somewhere, and I suspect it was by car. They didn't come up the road to town, so they must have used the road in the valley on the other side of the hill. I'm going to take a look. If there's a car there, I can at least get a license number. You watch 'em. If I'm not back by the time they cross to this side, don't worry. I won't get caught. Just go on home and wait for me."

Rick whispered an okay, and Scotty melted into the night with the noiseless skill that Rick so much admired. Then he turned his attention to the ghosts once more.

Rick counted five stops in various parts of the field. After the last one, the trio turned, recrossed the bridge, moving briskly, climbed the hill, and disappeared into the cornfield. Mission accomplished, apparently. What had the mission been?

According to Belsely, this happened each time, except for the occasion when a cart had been used. What were they hunting? Or, if they weren't hunting, what were they doing? Rick felt frustrated. To be so close, yet to be unable to see anything but vague shapes in the darkness!

Tomorrow he and Scotty would search both fields in an effort to find what the Blue Ghost sought, or to try to figure out what he and his friends were doing.

Scotty caught up with him as he was crossing the field by his plane. The dark-haired boy was triumphant. "They had a car, all right, and the registration was in a container on the steering wheel. I've got all the dope. Probably I shouldn't have done it, but I sneaked a quick look at the name. Can you imagine what it is?"

"Jethro Collins?"

"Nope. It's Hilleboe. Dr. Miller's next-door neighbor!"



CHAPTER XIV

The Cold, Cold Clue

The boys were late to breakfast the following morning. They had fallen into bed, pleased and exhausted, and the noise of the household stirring had failed to waken them.

Mrs. Miller greeted them as they came downstairs. "I hear you were ghost hunting again last night. Did you find any?"

"I'll say we did," Scotty replied. "Where is Dr. Miller?"

"Right here," the scientist said from the living-room doorway. "And I have news for you. Collins called this morning and renewed his offer. I told him I'd think about it and let him know later. And Steve Ames called. The powder is definitely carnotite, and it matches ore produced on the Colorado Plateau. Steve has reported to the Atomic Energy Commission, and they'll be able to track down its origin without too much difficulty, since no two ores are precisely alike. Now, how did you two do last night?"

The two girls came into the kitchen in time to hear the question, and Rick almost hated to give the answer, knowing that it would disillusion them, and particularly Barby.

"We trailed three ghosts," he said. "All human."

Scotty added, "And one of them was named Carleton Hilleboe. At least that was the name on the registration of their car."

They told the story in detail while Mrs. Miller and Jan fried eggs and bacon and made toast for their breakfast. Barby listened quietly, but if Rick had any idea she would be convinced, he was mistaken. When the recital ended she pointed out, "There's no reason why mortals shouldn't take advantage of a ghost. You still haven't proved that the ghost at the mine isn't real, or how the cold almost knocked you out last night."

"True," Rick had to admit. "We're not making much progress there."

Over breakfast Dr. Miller told them about the Hilleboes. "They were one of the big families in this vicinity two or three decades ago. They had the biggest house in this part of Virginia, but it burned down about twenty years ago and the kids moved away. There is no house on their land now. They rent some of the land to tenants. Carleton Hilleboe is the eldest son. He's in a business of some kind in Washington. He either controls or owns the property, I'm not sure which."

"Including the upland cornfield above the mine?" Rick asked.

"Yes, and all the property to the east of ours for a mile or two."

"Could he be the mysterious buyer Collins is acting for?" Rick asked.

"It's possible, although why he would want our share of the mine and the field opposite is beyond me. I think a talk with Collins is in order. If you two want to come to town with me, I think I'll beard him in his den. I've no intention of selling, but I won't tell him that."

On the way to town the boys agreed it would be best for Dr. Miller to talk with Collins alone. He obviously didn't like young people—at least them—and he would be more apt to confide in Dr. Miller if the scientist interviewed him alone.

The scientist agreed. "Why don't you two wait in the drugstore? You can have a coke or something."

Dr. Miller parked the car in front of Collins' house and the boys crossed the street to the drugstore. Although it was early in the day, both ordered a dish of ice cream. They were eating it and exchanging small talk with the druggist when the Frostola scooter pulled up outside. Both tensed as the Frostola man came in, but he greeted them impersonally and turned to the druggist. "I'd like a tin of aspirin, please."

"That infected hangnail still bothering you?" the druggist asked sympathetically.

"No, it's okay today," the peddler answered swiftly. "I've got a slight headache, that's all."

He paid for the aspirin, accepted the druggist's offer of a glass of water, downed two pills, and left.

"Seemed in a hurry," Rick commented.

The druggist nodded. "Seemed so. He usually stops to pass the time of day. Had a terrible time yesterday with an infected hangnail. They can be pretty painful. I tried to sell him a new analgesic ointment, but he insisted on methyl chloride. He had an old refillable prescription from some doctor over in Arlington. Said he got it because infected hangnails bother him all the time. Lucky I had some. It used to be used all the time for pain from superficial wounds, but it went out of style. He bought a whole pint. Enough to last for fifty hangnails. Told him he didn't need it, but he insisted."

Rick said thoughtfully, "His hands seemed to be all right today. No bandages."

"All he had was a plastic-tape bandage around his thumb yesterday, anyway. Guess the infection must have cleared up."

"What's methyl chloride?" Rick asked.

"A highly volatile chemical. It's not a painkiller in the usual sense, like aspirin. You spray it on the area that hurts, and it evaporates in seconds. You know what that does."

Rick did! And suddenly last night's events were perfectly, transparently clear.

"Evaporation cools the surface," Rick said for Scotty's benefit. "The faster the evaporation, the faster the cooling. This methyl chloride must act pretty fast."

"It does," the druggist agreed. "That's how it kills pain, partly. It chills the outer layer of skin almost instantly."



CHAPTER XV

The Missing Facts

Dr. Miller's conversation with Jethro Collins was something less than satisfactory. He told the boys about it on the way home.

"I told him bluntly that I was suspicious about his offer because the property he wants to buy has little value as farm land and contains no timber or anything else of commercial value. I told him I wouldn't consider an offer until I knew what the land was to be used for."

The scientist chuckled. "That was my way of putting him on a spot, of course. But he refused to be cornered. He replied that his customer wanted the land for reasons of his own, which it was not Collins' place to divulge. He assured me the land would not be used for commercial purposes, so my own property would be quite safe.

"I replied that I needed more assurances than his word, and demanded to know the identity of his client. I pointed out that the name would become known during the process of settlement anyway, unless his client proposed to use a dummy of some sort in which to register the deed to the land."

"But he wouldn't tell you the name," Rick guessed.

"Correct. My guess is that he would use a dummy of some sort, perhaps even Collins himself as nominal owner of the land."

Scotty offered, "People don't buy land unless it has some value for something. Can't you think of any way in which your land has value?"

"I'm afraid not. I've tried to puzzle it out, with no success. The field itself is all right, if fertilized and limed, but the rest is worthless for farming. There isn't even an access road. The road leading into the picnic area and across the creek to the house is my own property. It's a private road."

Rick kept wondering about the radioactive ore. "Could there be any minerals worth mining?"

"Not even that, Rick. Except for the igneous outcropping in which the mine is located, this whole valley is sedimentary rock, probably for a depth of several hundred feet. Even the foothills are the same kind of rock. They were moved upward from what is now the valley during a shift in the earth's crust. The faults in the formation show this clearly."

"The whole business is tied together somehow," Rick said with conviction. "So far we've been trying to follow threads. We come across other threads that seem to run crossways, but that's because what we're trying to see is a whole piece of cloth, not just the threads. So far we don't know if the cloth is a whole suit or just a handkerchief."

"The metaphor is a little obscure, but I get your meaning, and I agree." Dr. Miller drew to a stop in the driveway of his home. "Suppose we have a late morning bit of refreshment and use our heads instead of our legs?"

At the scientist's request, the girls produced a snack of toast and jam with iced tea and soft drinks. Mrs. Miller begged to be excused from the council because of housework to be done, but the others gathered in the living room to explore the mystery from every angle.

Dr. Miller led the discussion. The scientist was obviously intrigued by the problem, even though he had let the boys handle things in their own way. As he explained with a twinkle, "Rick and Scotty have reputations as detectives to maintain. I'm a poor, simple physicist. No one expects me to solve this mystery. So the boys have to be given first chance to bring the ghost to bay."

Barby sniffed. "You're all pretty sure the ghost is a fake."

"And you're not," Rick observed. "I guess we'll have to put him in a bottle for you before you'll believe it."

"Peace," Dr. Miller interposed. "Each to his or her own opinions. We're here in pursuit of facts, not fancies. Rick, you're first at bat."

Rick considered. What were the most important facts? They had been working on assumptions, but assumptions need proof before they can be accepted as valid.

"Well, I'm not sure I'm listing the facts in order of importance, but I'll try. First, the ghosts that walk the fields at night are humans."

Barby interrupted. "How can you be certain?"

"They looked human. We saw their silhouettes against the sky clearly enough to see their shapes, and they were human shapes." As she started to speak again, he held up his hand. "Whoa! Let me finish. Ghosts also have human shapes is probably your counterargument. I'm not arguing that ghosts don't really exist, but if they do, they are supposed to be sort of nonsolid, aren't they? Like the Blue Ghost at the mine. But the field ones were solid enough. No light showed through them."

"Not all ghosts are transparent," Barby insisted.

"She's got you." Dr. Miller chuckled.

Scotty spoke up. "Ghosts do not drive cars."

"And you've no proof the ghosts you saw in the field came from the car," Barby defended hotly. "Did you see them get in the car and drive away?"

Scotty held up his hands in surrender. "No. I passed them on my way back from the car."

"Evidence not sufficient," Dr. Miller said with a grin. "The ghosts may or may not be human. Your first fact needs more proof, Rick. Carry on."

Rick sighed. "All right. I'll start over again. First, we have uncovered cement bags that contained radioactive ore, pulverized into a fine dust. I'll amend that. The bags contain a small quantity of radioactive ore, which gives some reason for believing they were once full of such ore."

The group laughed. "Now you're on the beam," Dr. Miller approved. "State only what you know as fact and identify what you infer from the facts as inference or speculation."

"Glad you all approve. Second, we believe the Frostola man was interested in the cement bag Scotty carried. It is a fact that when we returned from town the cement bag that we put in the trash can, and the cement bags we left where we found them, had been removed. Because of the Frostola man's apparent interest, we are of the opinion he took the bags."

Jan Miller giggled. "You sound like a lawyer."

"I feel like one," Rick returned with a grin.

"Third, the Blue Ghost led Scotty and me on a wild chase that ended up with me dropping into the quarry. The facts are that the ghost somehow triggered the plane alarm. We will not argue whether or not a real ghost could have set off a purely physical, nonspiritual alarm."

Barby nodded soberly, but there was a twinkle in her blue eyes.

"Continuing with the facts of that incident, the ghost stayed ahead of us without difficulty. A real ghost could have done that, I suppose, but so could any person in reasonable physical shape who knew the terrain. Now, the ghost's light went off as he reached the edge of the quarry, or somewhere in the vicinity of the edge."

Rick looked at his sister. "I will stipulate that a real ghost need not have any reason for his actions. But a person imitating a ghost would have had to turn off his light in order to go around the quarry, otherwise we would have seen that he made a detour. A ghost would presumably float right over the quarry."

"Ghosts do float," Barby agreed solemnly.

"Uh-uh. Since this one did not, and since it reappeared—or the light did—on the opposite side of the quarry, we believe there was a deliberate attempt to lead us into said quarry."

He paused and took a deep breath. "How am I doing, coach?"

Dr. Miller nodded approval. "Fine. See how easy it is to separate fact and conjecture?"

"So what do we conclude from this one event? We conclude it is reasonable to believe that a person, and not a spook, triggered the plane alarm and led us to the quarry. We speculate that the person did not know about the alarm and set it off by accident, probably while inspecting the plane, since we see nothing to be gained by sabotage. We speculate that the chase was to frighten us, not primarily to harm us, the reason being that we rushed the ghost during the ghost act and are therefore potentially dangerous. We reach this conclusion because the ghost picked a side of the quarry where we would land in the water, which is plenty deep by the way, and not on the rocks."

"Okay. Scotty, take over. I'm worn out from trying to be precise."

The scientist grinned. "Lack of practice, I'm afraid. If we all sought precision in our speech many of the world's misunderstandings could be avoided."

"I don't know what we can say," Scotty objected. "We have few facts. We have only some observations. We can try to interpret our observations, but we can't prove them. For instance, there is the fact that we were given a bath of something by the Blue Ghost that seemed to freeze our faces. There is the fact that the Frostola man bought a quantity of methyl chloride. There is the fact that methyl chloride could have produced the effect we felt. But how can we say that it's a fact that the Frostola man somehow doused us with chemical?"

"You can't," Jan Miller agreed.

"So if we stick to demonstrable facts, we don't get far," the scientist concluded. "But can we settle for mere speculation?"

"No, sir," Rick stated. "But let's admit that speculation has its uses. After all, circumstantial evidence is permitted in court. Speculation can give us the circumstances that need to be proved, and that tells us where to put our efforts. I think that's fair enough."

"So do I," Dr. Miller agreed.

Rick arose. "Then we'll continue working the way we've been doing it. It's not the best way, but at least we're uncovering little items that can be tied together if we find just two missing facts."

"Like what?" Barby demanded.

"We go back to our assumption that the ghost is man-made. On this assumption, the things we need to know are how and why is the ghost produced?"



CHAPTER XVI

Trapped!

It was, as Rick said, time for action and not for words. He and Scotty set out to track down every possible shred of evidence. They armed themselves with flashlights, and Rick made sure he had his pocket lens, and they started out.

The first stop was in the field, to locate the places where last night's ghostly party had paused.

As the boys walked across the field toward the plane, Rick wondered aloud. "What did the ghost want with the plane?"

"Sabotage?" Scotty asked.

"Maybe. But if so, why?"

"Because he was afraid of what we might see from the air, maybe."

Rick considered. "It could be, I suppose, but we've examined the whole area from the plane. I didn't see anything suspicious or particularly interesting."

"Not a thing," Scotty confirmed. "But it might be a good idea to take another look."

"Okay. We can do it later this afternoon. Now, according to what I remember, the first stop the ghosts made was right about here. Let's work like hunting dogs and see what we can turn up."

Rick dropped his handkerchief on a clump of bachelor's-buttons for a marker, then he and Scotty walked in ever-widening circles, scanning the ground for any trace of the ghosts.

Scotty's keen eyes saw the first sign, a heelprint in a bare place in the grass. The boys examined it. "Doesn't match anyone's shoes," Scotty said. "Not of our gang. Leather heels, a little worn, run down on the outside edge. You can see the nail marks. No rubber heels would make those marks."

There were other prints, now that they were searching closely. Clearly, three men had walked the field last night. But nowhere did they find a clue to what the men had searched for. There was no raw dirt, no impressions left where something had been removed.

"Fact," Rick stated. "Three men were here."

Scotty laughed. "This does not mean there were not also three ghosts who left no tracks."

Rick had to laugh, too. "Now what do we do?"

"Look in the upland cornfield."

They started the survey of the cornfield directly above the mine entrance, where they had first seen the three ghosts. Tracks were visible almost at once.

"We're lucky," Scotty said. "Even with the weeds between the rows there's enough bare ground so we can do some real tracking. Let's see how the tracks run."

As Scotty had predicted, the tracking was much easier. A few yards into the cornfield they came to a gap where a few seeds had failed to germinate or the plants had died. It was a bare space, sparsely grown with weeds.

Scotty pointed to the three sets of tracks, and put his own feet in one set, while Rick did the same with another set. From the position of the third set it was clear that the three men had faced each other.

Rick said excitedly, "They paused and bent over. But over what?"

They scrutinized the ground minutely. It seemed normal enough. There was absolutely no sign that the earth had been disturbed.

Rick picked up a handful of soil and examined it. "Dirt," he said. "Plain dirt. Why was it so interesting to the spooks?"

"Try your lens," Scotty reminded him.

Rick did so. The lens showed the usual combination of mineral and organic matter of various sizes and colors. "I can't see anything unusual," he reported. "Maybe the lens isn't powerful enough. I'll take a sample and look at it under the microscope later." He found a scrap of paper in his wallet and folded a bit of dirt into it.

"Let's continue," Scotty urged.

They worked their way across the cornfield, following the tracks. Twice more they found places where the ghosts had paused to confer about something, or examine something.

Then, at the edge of the cornfield, they lost the tracks in a rank growth of weeds. Probably the ghosts had trampled the weeds last night, but they had sprung up again and left no trace of the passage.

Scotty took the lead. "I'll show you where the car was parked."

They traveled through alternate weeds and hay to where the hilltop dropped away rapidly to a valley about three hundred feet below. This marked the end of the igneous outcropping in which the lead mine was located, Rick guessed. The hill was steep, and overgrown with blackberry bushes.

"I got caught a thousand times in as many feet last night," Scotty commented. "It's easy by day, but don't try it by night." He led the way through clear spaces between the thorny patches, always going downhill.

It wasn't long before Rick saw the road, if it could be called that. It was two ruts with grass growing between them.

"Doesn't look like U.S. Highway Number 66," he remarked.

"There's a man who thinks it is," Scotty replied.

Rick looked to where his pal pointed. The Frostola man was approaching on his scooter. The sound of the little motor was just audible, and Rick's first impulse was to duck, but Scotty said, "Too late. He saw us just as we saw him. Let's walk down to the road and make it casual."

They did so, and the peddler approached, bumping over the uneven surface.

"Howdy," he greeted them. "Where does this road go?"

"We don't know," Scotty replied.

Rick added, "We're strangers in the area."

"I'm pretty new myself," the man said cheerfully. "Saw this road and thought there might be a settlement where I could find some new customers."

"We don't know of any," Rick said.

"Looks like I might as well go back to town, then. Want a lift? You can hang onto the step behind me."

"No, thanks," Scotty replied. "We're staying just over the hill."

The Frostola man turned his scooter wagon, gave them a wave, and went on his way back toward town. The boys watched until he drove out of sight.

"There's an optimist," Scotty said. "Follows a pair of ruts, hoping to find civilization at the other end."

Rick grinned. "He certainly likes this part of Virginia. There's one thing about peddling Frostola here—"

"What's that?"

"No customers to bother you. It's easy to commune with Nature."

"Aye-aye. Does he look like a nature lover to you?"

"Now that you mention it, I've seen people who fitted the part better. We scared him away, that's for sure. But what was he doing here?"

Scotty considered. "If he wanted to reach the mine area without people noticing him, he could park his scooter here and walk over the hill."

"He could," Rick agreed. "But why would he want to reach the mine area?"

"Not to sell Frostola. That's for sure."

"Uh-uh. My guess is he has to reset the Blue Ghost."

"Reset it?"

"Sure. Think about it. The projector can't go on operating forever when a clock reaches nine, can it? It must need servicing and resetting."

"And loading with methyl chloride to squirt at us?"

"Too true." Rick had wondered about that. "But how does the chemical squirter work? Where is it? The projector must be close to the Blue Ghost, if the chemical came from the same place."

Scotty laughed. "You don't discourage easily, do you? We tried to find a projector beam the other night, remember? What did we get for it? A squirt in the face. No projector, no nothing."

"There has to be a projector, or an imagemaker of some kind," Rick insisted, "unless you're admitting the ghost is real."

"Where would it be located?"

"Very close, I'd guess. Hidden somewhere near the spring pool, batteries and all. It has to be, and I think we'd better spend some time looking."

"Starting where? Don't tell me—it has to be the mine."

Rick was already walking back up the hill toward the cornfield. "There's no other underground location in which a projector could be stored, is there? So let's get at it."

"Glad we brought flashlights," was Scotty's only comment.

They hiked in silence to the cornfield, pausing now and then among the corn plants to examine footprints. Thanks to the rain that had left the ground soft, there were plenty of them, but they told the boys no more than they already knew.

At the top of the hill above the mine they paused to survey the scene. Belsely was hauling a load of rock through the field near the plane, using his tractor and a stoneboat. The boys knew he was busy building a stone fence. He saw them and waved. They waved back, then went down the hill to the spring and its basin.

Again they examined the entire location with great care, and Scotty probed seams in the rock with his jackknife blade. The entire hillside in this location was cracked and seamed and the rock face above the basin was rough and irregular. Rick wondered if there had ever been an earthquake in the neighborhood or whether the settling of the earth into the mine has caused the cracking.

"Nothing here," Scotty said. "At least nothing I can see. We'll have to try the mine itself."

They had replaced the boards at the entrance, simply pushing the nails back into the holes from which they had come. They pulled the boards aside and saw footprints—and not their own!

"Visitor," Scotty said with excitement.

Rick noted the size of the tracks. "And a big-footed one, too. Makes our tracks look small."

Scotty pointed. "He came out again, whoever he was. Let's see how far he went in."

The tracks told the story clearly and quickly. The visitor had gone in about twenty feet, and had then returned to the outside. One glance told the boys why.

The mine was timbered, with uprights and overhead beams spaced about every ten feet. Where the visitor had stopped, the mine timbers were supporting a big piece—or many pieces—of the rock overhead. Rick guessed that the heavy rain, working through cracks, had loosened a section and let its weight fall on the overhead crosspiece. It was also clear that the timbers would not support the weight for very long. They were rotten, and wet with the constant seepage of water.

"Must have been one of the Sons of the Old Dominion who wandered in for a look," Rick suggested. "He saw it wasn't safe and went right out again."

"Something like that," Scotty agreed. "And it isn't safe. Those timbers would go if anyone breathed hard at them."

"Then let's not breathe hard," Rick said.

"Meaning that we're going in, anyway."

Rick pointed out, with what he thought was complete logic, that the timbers had held the roof up since the rain, and that collapse surely wouldn't take place in a minute or two. He concluded, "And if we're going to find any kind of clue to a projector, it has to be in this mine somewhere."

"Then let's not linger," Scotty said. "And for Pete's sake don't stamp your feet when you go by the timbers. A little vibration would send them down for sure."

Rick asked, "What were the wind and the laughter the last time we were in here?"

"Imagination," Scotty replied. "Let's keep it under control this time."

"I'm with you. And ghosts don't blow out flashlights, so let's go."

They moved cautiously past the unsafe place, lights probing the tunnel walls for a sign of anything unusual or worthy of attention. Now and then they reached a bay where ore had been taken out, or a jog in the tunnel where the miners had lost the ore vein temporarily. They reached the spot of their penetration into the mine on their last visit and found the remains of their torches.

"No change. Thought they might have been chewed by ghosts," Scotty commented.

"Newsprint doesn't taste good," Rick replied. "Do ghosts have teeth?"

"Nope, just an icy breath. Do you remember any smell, by the way? When we got hit in our faces?"

"Something sort of sweet?"

"Yes. I wasn't thinking about smelling, and I didn't notice especially, but I sort of recall a nice odor."

Rick thought he remembered it, too. "We'll look up methyl chloride in the dictionary," he promised. "That will tell us if it has an odor."

The mine took a sharp turn. "They lost the vein here and had to chew out some rock to find it again," Rick pointed out. "Notice everything is on one level? Must have been just one vein. It ran out and the mine closed down."

"Looks that way," Scotty agreed. "How far have we come?"

Rick hadn't kept track, but he estimated they were perhaps halfway under the hill. "This must end somewhere," he said. "Notice there isn't any water at all, not even seepage? I'm still baffled by that spring and the pipe."

They traversed another hundred yards in silence, flashlights constantly scanning the mine. There was nothing out of the ordinary, no sign of ghost, projector, or even of human visitation for dozens of years.

"We're on another wild-goose..." Rick began. He never finished, for sound suddenly reverberated through the mine, the sound of rock crashing downward.

Both boys turned and ran back toward the entrance, afraid of what they would find. Long before they reached it, billowing clouds of dust told them what had happened.

Their racing legs confirmed it as they came to a stop against rock that choked the tunnel from top to bottom.



The timbers had given way. They were trapped!



CHAPTER XVII

In Darkness

For one despairing instant the two peered at the fallen rock through the thick haze of dust, then Scotty snapped, "Back into clean air."

They retreated the way they had come. Rick clicked off his flashlight instinctively. They might need it.

When clean air was reached again they stopped and Scotty swept his flashlight beam over the rocky floor. "Pick a seat and get comfortable. We'll be here for a while."

"We won't get out of here by sitting down," Rick replied.

"No, and we won't do much until the dust settles, either. Relax and get cooled off. When the dust has settled a little, we can go back and see just how bad the block is."

Rick remembered the tons of rock above the timbers. The block had to be bad, he thought. There was plenty of rock there. Then, as he thought about it, he wasn't so sure. A pretty large area had shown cracks, but perhaps only a layer had fallen. They might be able to dig out. Nothing to do about it but wait and see.

Scotty switched off his light and the blackness closed in. Rick shifted uncomfortably. Once before he had been lost in complete blackness like this, in the Caves of Fear. But that had been different; he hadn't been exactly trapped in the same way then, and the caves had covered miles under a Tibetan mountain. At least he knew exactly where he was this time.

He said, "We should have brought a picnic lunch."

Scotty chuckled, but didn't reply.

Rick said, "Suppose we can't get out?"

"We will. Dr. Miller will be hunting for us sooner or later. He couldn't miss the mine, especially with the boards off the entrance."

"Then all we need is patience and a tight belt."

"That's it."

The boys fell silent. Rick was cheered by Scotty's estimate of the situation. He closed his eyes, and for perhaps the hundredth time started mulling over the chain of events, searching for a clue to the two things they needed to know: how and why the ghost was produced.

But as he thought about it he wondered if perhaps they didn't know why. The ghost was a means of keeping people out of the area. It had succeeded to a considerable degree. There were no more night family picnics and swimming parties. There were only occasional long-scheduled events.

He explored the idea. The mine area was private property. To keep people out one would need only to post "No Trespassing" signs. But in all probability that wouldn't be suitable, because it would raise too many questions, and Dr. Miller would have to be let in on the secret of the ghosts that walked the fields.

But why keep people out of the area? To be sure, privacy for the conduct of secret operations was an obvious reason, only what were the secret operations, and why did they have to be kept secret?

He gave up finally. There simply weren't enough data on which to hang a conclusion.

"Think the dust has settled?" he asked.

"Could be. Suppose we go take a look. I'll use my light. Save yours."

They followed the yellow beam of Scotty's flashlight through the dark tunnel to the rockfall. There was still plenty of dust in the air, but it was bearable.

Scotty flashed his light on the timbers, then on the rockslide. One pair of uprights arose from the sloping pile of rock to a sound crosspiece.

Both boys knew what that meant. Rick put it into words. "If that's the set of timbers nearest to the ones that were bad, it means at least ten feet of rock on this side, and probably the same or even more on the other. A total of twenty feet of rock."

Scotty grunted. "One thing is for sure. We won't dig our own way out for a few days. I'm not even sure we can. We might collapse from lack of water if we try working real hard."

"But we can't wait for help from the outside," Rick pointed out. "We can at least work while we still have our health."

"Can you work in the darkness?"

"I suppose we'll have to. The lights won't last long."

"Then let's get to it."

They retreated to an alcove and put their shirts in a safe place, then went to work in their T shirts. Lugging rocks would work up a sweat, and it was chilly underground. The shirts were for use during rest periods.

"Let's see how it goes," Scotty invited, and turned off his light.

Rick groped for a rock and found a good-sized one. He carried it back and promptly bumped into a wall and dropped it. Keeping a straight line was going to be a problem. He groped for the rock and found it again, but this time he tucked it under one arm, using the opposite hand to guide him along the wall.

"I'm on the right-hand wall," he told Scotty. "I'll return along the left-hand wall."

"Good system," Scotty approved.

It was, too. They passed each other in the dark and Rick was pleased, until he tripped on a rock and stumbled into the pile.

"We're going to have to count paces," he said ruefully as he nursed a bruised knee. "Say twenty paces up and twenty paces back."

"Better make it twice that," Scotty replied. "We can't pile all the rocks in one place. We'll have to spread them out."

"Forty it is," Rick agreed, and found another rock.

The work went on, gradually assuming the proportions of a dream—or a nightmare. Pick up a rock, tote it forty paces, drop it. Then thirty-five paces as the passageway got cluttered. Now and then they had to join forces to lug a particularly big piece.

Rick's watch showed him that two hours had gone by. "Let's take a break," he suggested.

"Okay."

Scotty turned on his light. They found their shirts, then went back to survey what they had accomplished.

One glance told them it wasn't much. They had cleaned out the passage up to the main slide, and that was all.

They looked at each other in the flashlight's glow.

"Got any earth-moving equipment in your pocket?" Rick asked wryly.

"Not a dragline or a clamshell," Scotty said. "We certainly didn't make much of a dent, did we?"

"At this rate we'll be here until Christmas," Rick said.

"Not that we'll need a Christmas tree."

"We could use the lights," Rick commented. "Let's keep plugging. I'm not so sure I need a rest after all."

"Might as well."

"Just sitting on the rocks will sap our strength, anyway," Rick pointed out. "We might as well work while we're still fresh. We can take five-minute breaks when we begin to tire."

"I'm with you. Tote those rocks."

"Let's use one light, too. No point in just clearing the tunnel. We want to break through in as short a time as possible. If we use the light we can pull rocks from nearer the top of the slide."

"Sensible as usual. I'll prop my light so it shines on the slide."

Scotty did so, then both boys shed their shirts once more.

The rock hauling went faster even with the rays of the single flashlight. They took turns climbing the slide and throwing rocks down. The boy taking a turn at the bottom moved them out of the way.

"Watch it!" Rick yelled suddenly, and jumped away from a slide of rock. Scotty, who was back in the tunnel disposing of a big rock, asked anxiously, "Are you hurt?"

"No. Hand me that light, will you?"

Scotty carried the light to where Rick waited. Rick took it and shone it upward to where the slide had come from. He whistled. There was solid ceiling, but it was a yard higher than the rest of the tunnel ceiling.

He calculated quickly. "If this is typical, we have rock three feet thick, ten feet wide, and twenty feet long piled up in front of us. That makes six hundred cubic feet of rock."

"But it can't be typical," Scotty disagreed. "If three feet had fallen uniformly, it wouldn't have filled the tunnel. It must be much thicker right over the broken timbers."

"Not a very cheerful prospect, is it?" Rick had a vision of yards of rock ahead.

"I've seen happier prospects. But what can we do? Keep plugging is all, and hope it doesn't take long for Dr. Miller to locate us."

Rick looked at his watch. "No chance of that yet. It isn't even suppertime. It may be morning before Dr. Miller gets really worried."

Scotty chuckled grimly. "Our own reputation for being able to take care of ourselves is not helping us, either."

"I'll never go into a place without two entrances again," Rick promised.

There was a moment's shocked silence while the boys stared at each other. They spoke simultaneously.

"How do you know this has only one entrance?"

"How do we know this hasn't two entrances?"

They had never reached the end of the mine. For all they knew, it might only be necessary to walk out!

"We'll go see," Rick stated. "Right now."

"Didn't we ever ask about another entrance?" Scotty demanded.

"No, now that I think of it, and no one ever said anything about it."

"Maybe they never said anything because there isn't anything to say."

"No more assumptions," Rick said. "We can find out for ourselves. Get your shirt on and let's go."

They quickly dressed and hiked down the long tunnel to the point they had reached when the cave-in occurred. Rick paid more attention to the formation than before, and found it was easy to trace the ore vein. Pockets in the walls showed where offshoots of the main ore vein had been located and dug out, but mostly the mine bored through the hill in one continuous tunnel.

"Funny they didn't take more ore out of the top," Scotty commented. "Looks like fairly decent stuff overhead and to the left."

"Not good enough, I guess. Refining was pretty primitive in those days. Techniques are better now, but there probably isn't enough good ore here to make new operations worth the expense of getting it out."

"Look ahead," Scotty said.

Rick had been examining the wall of the tunnel. He turned and looked to where Scotty pointed, and his heart sank. It was another rockslide.

"Funny," Scotty commented. "The tunnel goes uphill to the slide."

Rick saw that his pal was right. But the change in elevation of the tunnel didn't seem important compared to the prospect that now faced them. They simply had to go back and resume their rock hauling. There was no way of knowing whether the tunnel continued beyond the slide, or whether the slide itself was the reason the Civil War miners had gone no farther.

"I need a rest," Rick said, discouraged. "Let's sit down and take a breather before we start back."

"Okay. Douse the light?"

"Might as well. Your battery's getting low."

Scotty switched the light off and they sat down on the hard rock floor. Rick closed his eyes and breathed deeply. Plenty of hard work ahead. He might as well rest while he could.

Scotty spoke suddenly. "Plenty of good fresh air down here. Isn't that a little odd?"

Rick stirred. "Is it? I hadn't thought much about it. But I suppose the air ought to be stale and smelly."

"Wet your finger."

"Huh? Oh, okay." It was the ancient trick of using the cooling caused by evaporation of moisture from a damp finger to show the movement of air currents. Rick let out an exclamation. The air in the tunnel was in motion!

Scotty said with suppressed excitement, "Close your eyes. I'm going to light a match."

Rick did so, and saw the light even through closed eyelids because his pupils were fully dilated. He opened his eyes cautiously, squinting against the glare of the match. As the pupils contracted he saw that the paper match burned brightly, and that the flame flickered!

Scotty jumped to his feet, switching on the flashlight. "The breeze is coming from the slide!"

With one accord they rushed to the slide and began pulling rocks away. Clearly, the tunnel sloped upward at this point. The question was, did it emerge in a real opening, or only in a hole driven through for ventilation?

There was only one way to find out: move rock!

They sought for key rocks, those that would allow other rocks to tumble down and out of the way.

Rick thought it was at least to their credit that they learned from experience. Then, as he jumped frantically to escape a sliding boulder, he had to grin at his own thought. They had learned, but not enough.

There was no doubt about it, a current of air came through the slide. They could feel it, cool and fresh, and redoubled their efforts.

Finally they had to slow down from sheer exhaustion.

"Take a break," Rick said huskily. "We'd be foolish to wear ourselves out."

"You're right." Scotty slumped down where he was and wiped his face. "That air current is getting stronger. We're making progress."

"Wish I knew toward what," Rick said.

"Air, anyway. And where there's a source of air is also daylight."

"I'd feel better if I could see some."

They rested in silence for five minutes by Rick's watch, then resumed, working as close to the top of the pile as they could get.

Scotty suddenly let out a yell, and Rick dodged to escape another rock, then leaped down as the whole pile crumbled. The rocks didn't fall far.

"Look," Scotty said breathlessly.

Rick turned on his own light to supplement the dim beam of Scotty's. Blackness yawned at the top of the slide!

Scotty was first through the hole, but Rick was right behind him. They emerged in a continuation of the tunnel, but on a higher level. Their lights showed that the tunnel continued.

They followed it for perhaps fifty feet, and found themselves in a cross tunnel in which their tunnel ended.

Scotty looked at Rick in the beam of the flashlight.

"We're somewhere," he said. "But where?"

Rick grinned. There was a definite breeze blowing, and he knew the outside and safety were not far away. "We're in the mine, under the same old hill. Soon as we find the source of that breeze, I'll identify our position within two feet."

Scotty returned the grin. "What are we waiting for? Let's go!"



CHAPTER XVIII

The First Fact

Rick said, "Hold it a minute. Which way do we go? If we assume the tunnel we came out of was fairly constant in direction, we should turn right to come out on the side of the hill where we saw the Frostola man a while ago. If we turn left, we go deeper into the hill."

Both boys saw the implication the moment the words left Rick's lips. "Right it is," Rick added quickly. "First thing we have to do is see if there really is a way out."

They turned right into the cross tunnel, and met the breeze head on. So long as they followed the direction of the breeze, they were approaching the outside air.

Within a hundred feet they saw a glimmer of daylight and broke into a run. The glimmer became an opening, irregular in shape, but obviously big enough for an entrance.

"We made it!" Rick exulted. "Let's get a good look at that sunshine!"

"Careful," Scotty cautioned. "We'll have to let our eyes adjust fully or the glare will hurt. Besides, it may not be a good idea to go barging out into the open. Might be some ghosts hanging around."

"You're right. Anyway, let's take a brief look. What's blocking the opening?"

As they approached he saw that it was the trunk of a fallen tree, festooned with blackberry bushes. When they looked through the entrance, blinking in the light, they saw that the tree wasn't really a block, because there was plenty of room to crawl out of the tunnel.

"That trunk makes a mighty good shield," Scotty said thoughtfully. "Bet this entrance is invisible ten feet away, except from the air!"

"And I'll add my own bet, that the entrance is very close to where we met the Frostola man this morning, and that he wonders if we spotted it from the plane."

Scotty shook his head. "No betting on sure things. This explains the interest in the plane, all right. Stand by, old son. I'm going to make a quick recon and be sure the coast is clear."

"Okay. Eyes adjusted?"

"Enough." Scotty went through the entrance on hands and knees. Rick saw his legs as he stood up and surveyed the scene.

"Come on out," Scotty called. "We're alone."

Rick joined him. The fallen tree trunk came above their knees. As Scotty had said, it made an effective shield for the mine entrance.

Rick studied the entrance itself. Probably it had once been a regular timbered entrance, like the one on the other side of the hill, but it had fallen in, the rocks wedging to form a low passage into the tunnel inside. The whole hillside was overgrown with brambles, down to the two-rut road below them, almost at the place where they had met the peddler.

"We were within fifty feet of this entrance," Rick said, "and never suspected it."

"The Frostola man knew it. Do you think he thought we knew it?"

"Possible, I suppose. I'm not so interested in what he thinks as I am in what he was doing here. Where would we have ended if we had taken the left-hand turn, do you suppose?"