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 clown into the tunnel. It's the incandescent lights I see. I can look right at the ledge of rock where I kept watch that day, and where I saw--where I saw the face of Waddington!" he cried. "It wasn't a dream after all. This is a shaft connecting with the tunnel. We didn't discover it because this rock fits right in the opening in the roof. It must have been there all the while, and some blast brought it to light. Is this how the men got out, or were taken out of the tunnel, Masni?" Tom asked.

"This how," said the Indian woman. "See, here rope!"

She pawed aside a mound of earth, and disclosed a rope buried there, a rope knotted at intervals. This, let down through the hole in the roof of the tunnel, provided a means of escape, and in such a manner that the disappearance of the men was most mysterious.

"I see how it is!" cried Tom. "Some one interested, Waddington probably, who knew about this old secret shaft going down into the earth, used it as soon as our blasting was opened that far. They got the men out this way, and hid them in the secret valley."

"But what for?" cried Mr. Damon.

"To cripple us! To cause the strike by making our other workers afraid of some evil spirit! The men were taken away secretly, and, doubtless, have been kept in idleness ever since--paid to stay away so the mystery would be all the deeper. Our rivals finding they couldn't stop us in any other way have taken our laborers away from us."

"Bless my meal ticket! It does look like that!" cried Mr. Damon.

"Of course that's the secret!" cried Tom. "Blakeson & Grinder, or some of their tools--probably the bearded man or Waddington--found out about this shaft which led down into our tunnel. They induced the first ten men to quit, and when Tim went to get the fuse the rope was let down, and the men climbed up here, one after the other. Those Indians can climb like cats. Once the ten were out the shaft was closed with the rock, and the ten men taken off to the valley to be secreted there.

"The same was done with the next fifteen, and, I suppose, if the strike hadn't come, more of our workers would have been induced to leave in this way. They're probably being better paid than when earning their wages; and their relatives must know where they are, and also be given a bonus to keep still. No wonder they didn't make a fuss.

"And no wonder we couldn't find any opening in the tunnel roof. This rock must fit in as smoothly as a secret drawer in the kind of old desk where missing wills are found in stories."

"You say you saw Waddington, or the bearded man?" asked Mr. Damon.

"At the time," replied Tom, "I thought it was a dream. Now I know it wasn't. He must have opened the shaft just as I awakened from a doze. He saw me and closed it again. He may have been getting ready then to take off more of our men, so as to scare the others. Well, we've found out the trick."

"And what are you going to do next?" asked Mr. Dam~n.

"Get those missing men back. That will break the hoodoo, and the others will come back to work. Then we'll get on the trail of Wadding ton, or Blakeson & Grinder, and put a stop to this business. We know their secret now."

"You mean to get the men out of the secret valley, Tom?"

"Yes. There must be some other way into it than down the rock where we were. How about it, Masni?" and he inquired as to the valley. The Indian woman gave Tom to understand that there was another entrance.

"Well, close up this shaft now before some one sees us at it--the bearded man, for example," Tom suggested. He took another look down into the tunnel, which was now deserted on account of the strike, and then Masni pressed on the mechanism that worked the stone. She showed Tom how to do it.

"Just a counter-balanced rock operating on the same principle as does a window," Tom explained, after a brief examination. "Probably some of the old Indian tribes made this shaft for ceremonial purposes. They never dreamed we would drive a tunnel along at the bottom of it. The shaft probably opened into a cave, and one of our blasts made it part of the tunnel. Well, this is part of the secret, anyhow. Much obliged to you, Masni!"

The Indian woman had indeed revealed valuable information. They covered the secret rock with brush, as it had been, hid the rope and came away. But Tom knew how to find the place again.

Events moved rapidly from then on. The Titus brothers were more than astonished when Tom told them what he had learned. Masni had told him how to get into the secret valley by a round about, but easy trail, and thither Tom, the contractors, Mr. Damon and some of the white tunnel workers went the next day.

The sequestered men, taken completely by surprise, tried to bolt when they saw that they were discovered, and then, shamefacedly enough, admitted their part in the trick.

They would not, however, reveal who had helped them escape from the tunnel. Threats and promises of rewards were alike unavailing, but Tom and his employers knew well enough who it was. The tunnel workers seemed rather tired of living in comparative luxury and idleness, and agreed to come back to their labors.

They packed up their few belongings, mostly cooking pots and pans, and marched out of the valley to the village at Rimac.

And so the strike was broken.

The reappearance of the missing men, in better health and spirits than when they went away, acted like magic. The other men, who had missed their wages, crowded back into the shaft, and the sounds of picks and shovels were heard again in the tunnel.

Whether the missing ones told the real story, or whether they made up some tale to account for their absence, Tom and his friends could not learn. Nor did the bearded man (if he it were who had helped in the plot), nor any representative of Blakeson & Grinder appear. The work on the tunnel was resumed as if nothing had happened. But Tom arranged a bright light so it would reflect on the spot in the roof where the moving rock was, so that if the evil face of the bearded man, or of Waddington, appeared there again, it would quickly be seen. A search of the neighborhood, and diligent inquiries, failed to disclose the presence of any of the plotters.

And then, as if Fate was not making it hard enough for the tunnel contractors, they encountered more trouble. It was after Tom had set off a big blast that Tim Sullivan, after inspecting what had happened, came out to ask.

"I soy, Mr. Swift, why didn't yez use more powder?"

"More powder!" cried Tom. "Why, this is the most I have ever set off."

"Then somethin's wrong, sor. Fer there's only a little rock down. Come an' see fer yersilf."

Tom hastened in. As the foreman had said, the effect of the blast was small indeed. Only a little rock had been shaled off. Tom picked up some of this and took it outside for examination.

"Why, it's harder than the hardest flint we've found yet," he said. "The powder didn't make any impression on it at all. I'll have to use terrific charges."

This was done, but with little better effect. The explosive, powerful as it was, ate only a little way into the rock. Blast after blast had the same poor effect.

"This won't do," said Job Titus, despairingly, one day. "We aren't making any progress at all. There's a half mile of this rock, according to my calculations, and at this rate we'll be six months getting through it. By that time our limit will be up, and we'll be forced to give up the contract What can we do, Tom Swift?"