ight be," agreed the young fellow. "But if it is a cavern, where
under the sun is the mouth of it? How do they get in or out? It beats my
time!"

Ruth quickly acknowledged that the mystery was beyond her comprehension.
The sing-song sounds--for such they seemed to be--went on and on,
meaningless for the two listeners, who could not distinguish a single
word.

"Think that's your King of the Pipes?" asked Chessleigh finally.

"I don't know. If it is, there must be something more the matter with him
than Willie says there is. He sounds crazy--that is the way it sounds to
me."

CHAPTER XX

A FAILURE IN CALCULATION

"What shall we do now?" asked Ruth finally, and in a whisper.

"Let's go down to that place where we saw the boat land the other
morning," returned her companion. "I'd like to look about there a bit."

"Do you think it is wise?"

"I don't know about the wisdom of it," chuckled Chessleigh. "But I do
know that I'm not at all satisfied. Some people are here on the island,
and I'd like to know where they are."

"I am afraid we will get into trouble."

"If it is only that old man----"

"We don't know that it is. He must be talking to somebody--if that is his
voice we hear."

"Maybe he is only talking to himself. I don't hear anybody else," replied
the young fellow. "Come on. Let's see the thing through, now we have
started."

Indeed Ruth wanted to see it through. She was quite as curious as her
companion. So she made no further objection.

Pushing through the brush, they climbed carefully down the slope on the
outer side of the island. The landing where they had fastened their own
boat was on the inner side of the island, while this side fronted the
broad expanse of the river.

They could see the hurrying current, glinted here and there by the soft
starlight. Everything looked ghostly about them. The dim silvery light
made it possible for them to pick their way without stumbling. They made
little noise in reaching the shore.

There was a little indention here--a tiny cove. The shore was shelving,
and of sand and gravel. Chess pointed silently to the unmistakable marks
of a boat's bow in several places.

"That boat has been here more than once," he whispered.

Ruth breathed "Yes," but said no more.

Up-stream of the cove was a great mass of rock--not one rock, but several
huddled together and the cracks between overgrown with brush and vines.
Chess brought into use the electric torch