"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 c.o.ke 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 rea.s.sured 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 a.s.sume?"

"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 a.s.sumption 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 a.s.sume?"

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 c.o.ke 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 a.s.sumption 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 amus.e.m.e.nts 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 a.s.sumed 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 quant.i.ty 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?"