"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 pa.s.sed 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 a.s.sured 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 carnot.i.te, 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.