t espying the eavesdroppers. As for Nicolas, he had
vanished like the mist before the sun.

"Ha-ho-hum!" yawned Pedro Gato, audibly.

Tom raised his head, studying their immediate surroundings. He
soon fancied he saw a safe way of slipping off to the southward
and finding the road again below where Gato stood.

Signing to Hazelton, Reade rose softly and started off. Two or
three minutes later the young engineers were a hundred yards away
from Gato, though in a rock-littered field where a single incautious
step might betray them.

"Come on, now," whispered Tom. "Toward the mine."

"And run into Gato?" grimaced Harry. "Great!"

"If we meet him we ought to get away with him between us," Tom
retorted. "One of us did him up this morning."

"Go ahead, Tom!"

Reade led the way in the darkness. They skirted the road, though
keeping a sharp lookout.

"There are the lights of the mule-train ahead," whispered Tom.
"Now, we're close enough to see things, for there is _El Sombrero_
just ahead."

"What's the game, anyway?" whispered Harry.

"Surely you guess," protested Tom.

"Why, it seems that Don Luis is having ore from another mine brought
down in the dead of the night."

"Yes, and a lot of it," Tom went on. "Did you notice how much
rich ore there was in each tunnel to-day? And did you notice,
too, that when blasts were made with us looking on, no ore worthy
of the name was dug loose? Don Luis has been spending a lot of
money for ore with which to salt his own mine!"

"Salting" a mine consists of putting the gold into a mine to be
removed. Such salting gives a worthless mine the appearance of being
a very rich one.

"But why should Don Luis want to salt his own mine?" muttered
Harry.

"So that he can sell it, of course!"

"But he doesn't want to sell."

"He says he doesn't," Tom retorted, with scorn. "This afternoon,
you remember, he got me to copy a report in English about his
mine and then he wanted us to sign the report as engineers. Doesn't
that look as though he wanted to sell? Harry, Don Luis has buyers
in sight for his mine, and he'll sell it for a big profit provided
he can impose on the buyers!"

"What does he want us for, then? He spoke of engineering problems."

"Don Luis's engineering problem," uttered Tom Reade, with deep
scorn, "is simply to find two clean and honest engineers who'll
sign a lying report and enable him to swindle some man or group
of men out of a fortune."