ck'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