minute later perched itself on one of the decaying rafters.

"If there were any one around, they would certainly see Ab,"
reasoned Billie, "and would make some noise about it. I guess
it's safe to go in."

He crawled around to the door and entered. There were the tracks
of the horses, but the horses had disappeared as completely as
though they had been swallowed up.

Billie called softly to Ab, who did not see fit to obey until he
waved his whip. Then the animal sprang lightly to the ground.
Billie showed him the tracks.

"Where do you suppose they went?" he asked.

Ab blinked his eyes and, for the first time since Billie had
become acquainted with him, made a noise in his throat, much like
the voice of a child.

Billie smiled in spite of himself.

"I'm glad you've decided to become sociable," he said, "What do
you make of this? You look as though you could think."

Ab blinked his eyes stupidly and then suddenly became alert as
though listening.

"What is it?" asked Billie, impressed by the ape's attitude.

For a reply Ab sprang through the window and made straight for
the structure in the middle of the quarry. In another instant he
was on the roof.

Billie followed as fast as he could and as he stepped beneath the
roof started back in the utmost amazement, for up through what
looked like a huge well there came the distinct sound of human
voices.

For several seconds he stood as one in a spell and then he
started forward to peer into the well, but on a second thought
did not.

"I couldn't see anything if I did," he thought, "but any one
looking up could see me. I'll do better by listening."

The words came to him almost as distinctly as though he were in
the same room with the speakers, and there was no longer any
doubt that the voices were those of the Zapatistas who had
attempted to rob the train.

From their conversation Billie learned the outcome of the fight,
and he was greatly amused at the attempt of the bandits to figure
out who had betrayed them. Each one had a different theory, but
all agreed that there must have been a traitor in the band. It
was all the lad could do to prevent himself from calling out to
them, just to see what effect his words would have.

After discovering from the conversation that the bandits felt
themselves perfectly secure where they were and that they were
likely to stay there for some time, he finally decided to get
back to the railroad and thence to Pachuca a