Left to himself, with only the rather silent gang of Peruvian Indians as company, Tom Swift looked about him. There was not much active work to be done, only to see that the Indians filled the dump cars evenly full, so none of the broken rock would spill over the side and litter the tramway. Then, too, he had to keep the Indians up to the mark working, for these men were no different from any other, and they were just as inclined to "loaf on the job" when the eye of the "boss" was turned away.  
They did not talk much, murmuring among themselves now and then, and little of what they said was intelligible to Tom. But he knew enough of the language to give them orders, the main one of which was:
 
"Hurry up!"
 
Now, having seen to it that the gang of which he was in temporary charge was busily engaged, Tom had a chance to look about him. The tunnel was not new to him. Much of his time in the past month had been spent in its black depths, illuminated, more or less, by the string of incandescent lights.
 
"What I want to find," mused Tom, as he walked to and fro, "is the place where those Indians disappeared. For I'm positive they got away through some hole in this tunnel. They never came out the main entrance."
 
Tom held to this view in spite of the fact that nearly every one else believed the contrary—that the men had left by the tunnel mouth, near which Tom happened to be alone at the time.
 
Now, left to himself, with merely nominal duties, and so disguised that none of the workmen would know him for the trim young inventor who oversaw the preparing of the blast charges, Tom Swift walked to and fro, looking for some carefully hidden passage or shaft by means of which the men had got away.
 
"For it must be well hidden to have escaped observation so long," Tom decided. "And it must be a natural shaft, or hole, for we are boring into native rock, and it isn't likely that these Indians ever tried to make a tunnel here. There must be some natural fissure communicating with the outside of the mountain, in a place where no one would see the men coming out."
 
But though Tom believed this it was another matter to demonstrate his belief. In the intervals of seeing that the natives properly loaded the dump cars, and removed as much of the debris as possible, Tom looked carefully along the walls and roof of the tunnel thus far excavated.
 
There were cracks and fissures, it is true, but they were all superficial ones, as Tom ascertained by poking a long pole up into them.
 
"No getting out that way," he said, as he met with failure after failure.
 
Once, while thus engaged, he saw Serato, the Indian foreman looking narrowly at him, and Serato said something in his own language which Tom could not understand. But just then along came Tim Sullivan, who, grasping the situation, exclaimed:
 
"Thot's all roight, now, Serri, me lad!" for thus he contracted the Indian's name. "Thot's a new helper I have, a broth of a bye, an' yez kin kape yer hands off him. He's takin' orders from me!"
 
"Um!" grunted the Indian. "Wha for he fish in tunnel roof?" for Tom's pole was one like those the Indians used when, on off days, they emulated Izaak Walton.
 
"Fishin' is it!" exclaimed Tim. "Begorra 'tis flyin' fish he's after I'm thinkin'. Lave him alone though, Serri! I'm his boss!"
 
"Um!" grunted the Indian again, as he moved off into the farther darkness.
 
"Be careful, Tom," whispered the Irishman, when the native had gone. "These black imps is mighty suspicious. Maybe thot fellah had a hand in th' disappearances hisself."
 
"Maybe," admitted Tom. "He may get a percentage on all new hands that are hired."
 
Tom kept on with his search, always hoping he might find some hidden means of getting out of the tunnel. But as the days went by, and he discovered nothing, he began to despair.
 
"The queer thing about it," mused Tom, "is what has become of the ten men. Even if they did find some secret means of leaving, what has become of them? They couldn't completely disappear, and they have families and relatives that would make some sort of fuss if they were out of sight completely this long. I wonder if any inquiries have been made about them?"
 
When Tom came off duty he asked the Titus brothers whether or not any of the relatives of the missing men had come to seek news about them. None had.
 
"Then," said Tom, "you can depend on it the men are all right, and their relatives know it. I wonder how it would do to make inquiries at that end? Question some of the relatives."
 
"Bless my hat band!" exclaimed Mr. Damon, who was at the conference. "I never thought of that. I'll do it for you."
 
The odd man had gotten his quinine gathering business well under way now, and he had some spare time. So, with an interpreter who could be trusted, he went to the native village whence had come nearly all of the ten missing men. But though Mr. Damon found some of their relatives, the latter, with shrugs of their shoulders, declared they had seen nothing of the ones sought.
 
"And they didn't seem to worry much, either," reported Mr. Damon.
 
"Then we can depend on it," remarked Tom, "that the men are all right and their relatives know it. There's some conspiracy here."
 
So it seemed. But who was at the bottom of it?
 
"I can't figure out where Blakeson & Grinder come in," said Job Titus. "They would have an object in crippling us, but they seem to be working from the financial end, trying to make us fail there. I haven't seen any of their sneaking agents around here lately, and as for Waddington he seems to have stayed up North."
 
Tom resumed his vigil in the tunnel, poking here and there, but with little success. His week was about up, and he would soon have to resume his character as powder expert, for the debris was nearly all cleaned up, and another blast would have to be fired shortly.
 
"Well, I'm stumped!" Tom admitted, the day when he was to come on duty for the last time as a pretended foreman. "I've hunted all over, and I can't find any secret passage."
 
It was warm in the tunnel, and Tom, having seen one train of the dump cars loaded, sat down to rest on an elevated ledge of rock, where he had made a sort of easy chair for himself, with empty cement bags for cushions.
 
The heat, his weariness and the monotonous clank-cla............