off."

"They've shut off the motor," said Jack. "They must be going to land.
But where in the world could they land in these hills and in this
darkness, too?"

Tom Bodine slapped his knee.

"That's it," he said emphatically. "That must be it."

"What?" asked Jack.

"Why, there's a big level place just below the cave I was tellin' you
'bout. A plateau. Smooth as a floor."

The hum of the airplane had died away. The boys and their guide never
had caught sight of the machine in the darkness.

Suddenly Frank pointed in the direction whence the sound of the
airplane had come, ahead and slightly to the left.

"I thought I saw a light there," he whispered. "It was just a faint
streak of orange. Now it's gone."

"Look here," said Bob to Tom Bodine, "does that cave face this way or
is it on the other side of a hill?"

"It's on t'other side," answered Tom, "an' near the top."

"Well, I'll bet you there's somebody in that cave. And the light that
Frank saw was some kind of a signal to the airplane."

The big ex-cowboy scratched his head.

"Mebbe you're right," he said doubtfully. "I don't know 'bout such
things. But who'da thought that cave would be discovered. Why, I just
come on it accidental like onct when I was wanderin' through these
hills."

"Boys, there's only one thing to do," said Jack in a determined voice,
"and that's to investigate."

"Righto, Jack," said Frank eagerly. "Here's our chance to get back our
airplane."

"You said it," declared Bob. "Let's go."

"Not so fast," said Jack. "First we must have a plan of campaign.
Tom, what's the lay of the land? How far away is the cave? Would it be
better to leave our horses here and approach on foot?"

"Cave's not more'n half a mile from here," answered Tom. "It's just
around the shoulder o' this hill we're on right now and near the top.
I tole you 'bout that big rock in front o' the entrance an' them three
lonesome trees at the foot that give you a bee-line to the rock. Well,
we can git to them trees without bein' noticed an' tie our horses
there an' then sneak up afoot."

"Is there only the one entrance to the cave?"

"Only one," answered Tom. "There's a kind o' chimney up through the
rock to the top o' the hill. But nobody couldn't git out there in much
of a hurry. We won't have to worry 'bout that."

Frank had an idea.

"How far would those fellows in the airplane have to go to reach the
cave after landing?"

"Oh, le's see. 'Bout as fur a