“You may go to a quieter place,” nodded Gato.  “You know where—­the place I showed you this afternoon.  As for me, after the mule-train has left the mine, I must go there.  I will join you before daybreak.”

“We’ll go now, then,” muttered one of the men, rising.

They were coming up the road in the direction of the young engineers.  There was no time to retreat.  Tom glanced swiftly around.  Then he made a sign to Harry.  Both young engineers flattened themselves out behind a pile of stones at the roadside.  Their biding-place was far from being a safe one.  But four drowsy bandits plodded by without 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!”