e took command. "Don't fire without cause, however," he
whispered. "If there is someone behind us, it may be another
traveller."

Again came the sound of a horse stumbling. All heard it distinctly.
Jack peered into the darkness and called firmly:

"Who are you?"

"Challenge him in Spanish, why don't you?" muttered Frank.

Before Jack could repeat his challenge, however, a familiar voice
replied:

"That you, Jack? This is Tom."

"Tom? Tom Bodine?"

"The same," replied the ex-cowboy, materializing out of the darkness,
and approaching. "And glad I am," he added, "to find you."

"But, good gracious, Tom, is anything the matter? Why are you here? I
thought we left you heading back for home five hours ago?"

"No, you just left me," said Tom. "That's all. I didn't head home,
because I wanted to come along. Been a-trailin' you all the way. And
here I am."

Jack was surprised, indeed. But now that Tom was with them, he
experienced a sense of relief. To venture into a strange land without
a guide, and in pitch darkness, besides, was a pretty stiff
undertaking. The responsibility of looking after his friends was no
light one.

"To tell the truth, Tom," Jack said, "I'm glad you came."

Bob and Frank echoed his words heartily.

"I had just about decided when you came up," Jack added, "that I had
lost my way. Frank thought, however, we merely hadn't gone far enough
to find your landmarks."

"He was right," said Tom. "You come straight as a die. All we got to
do is to ride on a piece an' we'll be in the snuggest cave ever you
see."

Riding two abreast, Tom and Jack in the lead and Frank and Bob close
behind, they pressed on another twenty minutes when Tom called a halt
to indicate a clump of rocks close at hand which suggested in their
outline a crouching camel. Then he led the way toward the left.

"Wait, wait," called Bob, in a tense voice that reached the ears of
all, and caused them to halt. "Keep your horses quiet and listen.
There. I was right."

All sat silent, and distinctly there came to their ears the hum of an
approaching airplane.

CHAPTER XVII

INSIDE THE CAVE

"What is it?" whispered Tom Bodine, to whom the sound was unfamiliar.
"Sounds like machinery of some kind."

"It's an airplane," Jack answered.

"Airplane? _An_ airplane?" said Bob, low voiced. "It's better than
that. It's our airplane, if I know anything."

"Righto, Bob," agreed Frank. "I'd know the old baby's voice a mile