Calling to a girl of about thirteen years to look after her baby, Masni slipped along up a rough mountain trail, motioning to Tom, Mr. Damon and Koku to follow. Or rather, the woman gave the sign to Tom, ignoring the others, who, naturally, would not be left behind. Masni seemed to have eyes for no one but the young inventor, and the manner in which she looked at him showed the deep gratitude she felt toward him for having saved her baby from the great condor.  
"Come," she said, in her strange Indian tongue, which Tom could interpret well enough for himself now.
 
"But where are we going, Masni?" he asked. "This isn't the way to the tunnel."
 
"Me know. Not go to tunnel now," was her answer. "Me show you men."
 
"But which men do you mean, Masni?" inquired Tom. "The lost men, or the bad ones, who are making trouble for us? Which men do you mean?"
 
Masni only shook her head, and murmured: "Me show."
 
Probably Tom's attempt to talk her language was not sufficiently clear to her.
 
"My man—he good man," she said, coming to a pause on the rough trail after a climb which was not easy.
 
"Yes, I know he is," Tom said. "But he went on a strike with the others, Masni. He no work. He go on a 'hit,' as Serato calls it," and Tom laughed.
 
"My man he good man—but he 'fraid," said the wife. "He want to tell you of bad mans, but he 'fraid. You save my baby, I no 'fraid. I tell."
 
"Oh, I see," said Tom. "Your husband would have given away the secret, only he's afraid of the bad men. He likes me, too?"
 
"Sure!" Masni exclaimed. "He want tell, but 'fraid. He go 'way, I tell."
 
Tom was not quite sure what it all meant, but it seemed that after his slaying of the condor both parents were so filled with gratitude that they wanted to reveal some secret about the tunnel, only Masni's husband was afraid. She, however, had been braver.
 
"Something is going to happen," said Tom Swift. "I feel it in my bones!"
 
"Bless my porous plaster!" cried Mr. Damon. "I hope it isn't anything serious."
 
"We'll see," Tom went on.
 
They resumed their journey up the mountain trail. It wound in and out in a region none of them had before visited. Though it could not be far from the tunnel, it was almost a strange country to Tom.
 
Suddenly Masni stopped in a narrow gorge where the walls of rock rose high on either hand. She seemed looking for something. Her sharp, black eyes scanned the cliff and then with an exclamation of satisfaction she approached a certain place. With a quick motion she pulled aside a mass of tangled vines, and disclosed a path leading down through a V shaped crack in the cliff.
 
"Mans down there," she said. "You go look."
 
For a moment Tom hesitated. Was this a trap? If he and his friends entered this narrow and dark opening might not the Indian woman roll down some rock back of them, cutting off forever the way of escape?
 
Tom turned and looked at Masni. Then he was ashamed of his suspicion, for the honest black face, smiling at him, showed no trace of guile.
 
"You go—you see lost men," the woman urged.
 
"Come on!" cried Tom. "I believe we're on the track of the mystery!"
 
He led the way, followed by Mr. Damon, while Koku came next and then Masni. It could be no trap since she entered it herself.
 
The path widened, but not much. There was only room for one to walk at a time. The trail twisted and turned, and Tom was wondering how far it led, when, from behind him, came the cry of the woman:
 
"Watch now—no fall down."
 
Tom halted around a sharp turn, and stood transfixed at the sight which met his gaze. He found himself looking out through a crack in the face of a sheer stone cliff that went straight down for a hundred feet or more to a green-carpeted valley.
 
Tom was standing in a narrow cleft of rock—the same rock through which they had made their way. And at the foot of the cliff was a little encampment of Indians. There were a dozen huts, and wandering about them, or sitting in the shade, were a score or more of Indians.
 
"There men from tunnel," said Masni, and, as he looked, wondering, Tom saw some of the workers he knew. One especially, was a laborer who walked with a peculiar limp.
 
"The missing men!" gasped the young inventor.
 
"Bless my almanac!" cried Mr. Damon. "Where?"
 
"Here," answered Tom. "If you squeeze past me you can see them."
 
Mr. Damon did so.
 
"How did they get here?" asked the odd man, as he looked down in the little valley where the missing ones were sequestered.
 
"That's what we've got to find out," Tom said. "At any rate here they are, and they seem to be enjoying life while we've been worrying as to what had become of them. How did they get here, Masni?"
 
"Me show you. Come."
 
"Wait until I take another look," said Tom.
 
"Be careful they don't see you," cautioned Mr. Damon.
 
"They can't very well. The cleft is screened by bushes."
 
Tom looked down once more on the group of men who had so mysteriously disappeared. The little valley stretched out away from the face of the cliff, through which, by means of the crack, or cleft in it, Tom and the others had come. Tom looked down the wall of rock. It was as smooth as the side of a building, and offered no means of getting down or up. Doubtless there was an easier entrance to the valley on the other side. It was like looking down into some vast hall through an upper window or from a balcony.
 
"And those men have been in hiding, or been hidden here, ever since they disappeared from the tunnel," said Mr. Damon.
 
"It doesn't look as though they were detained by force," Tom remarked. "I think they are being paid to stay away. How did they get here, Masni?"
 
"Me show you. Come!"
 
They went back along the trail that led through the split in the rock, until they had come to the place where the natural curtain of vines concealed the entrance. Tom took particular notice of this place so he would know it again.
 
Then Masni led them over the mountain, and this time Tom saw that they were approaching the tunnel. He recognized some places where he had taken samples of rock from the outcropping to test the strength of his explosive.
 
Reaching a certain wild and desolate place, Masni made a signal of caution. She seemed to be listening intently. Then, as if satisfied there was no danger, she parted some bushes and glided in, motioning the others to follow.
 
"Now I wonder what's up," Tom mused.
 
He and the others were soon informed.
 
Masni stopped in front of a pile of brush. With a few vigorous motions of her arms she swept it aside and revealed a smooth slab of rock. In the centre was what seemed to be a block of metal Masni placed her foot on this and pressed heavily.
 
And those watching saw a strange thing.
 
The slab of rock tilted to one side, as if on a pivot, revealing a square opening which seemed to lead through solid stone. And at the far end of the opening Tom Swift saw a glimmer of light.
 
Stooping down, he looked through the hole thus strangely opened and what he saw caused him to cry out in wonder.
 
"It's the tunnel!" he cried. "I can look right ............