Hardly comprehending what the Irish foreman had said, Tom Swift, the Titus brothers and Mr. Damon followed Tim Sullivan back into the tunnel. They had not gone far before they heard the murmur of many voices, and mingled with that were roarings like those of wild beasts.

"That's thim!" cried Tim. "They're chawin' each other up!"

"Koku and that Indian giant fighting!" cried Tom. "What's it all about?"

"Don't ask me!" shouted Tim. "They've been on bad terms iver since they met." This was true enough, for one giant was jealous of the other's power, and they were continually trying feats of strength against one another. Probably this had culminated in a fight, Tom concluded.

"And it will be some fight!" mused the young inventor.

Hurrying on, Tom and his companions came upon a strange and not altogether pleasant sight. In an open place in the tunnel, where the lights were brightest, and in front of the rocky wall which offered a bar to further progress and which was soon to be blasted away, struggled the two giants.

With their arms locked about one another, they swayed this way and that--a struggle between two Titans. Of nearly the same height and bigness, it was a wrestling match such as had never been seen before. Had it been merely a friendly test of strength it would have been good to look upon. But it needed only a glance into the faces of either giant to show that it was a struggle in deadly earnest.

Back and forth they reeled over the rocky floor of the tunnel, bones and sinews cracking. One sought to throw the other, and first, as Koku would gain a slight advantage, his friends would call encouragement, while, when Lamos seemed about to triumph, the Indians favoring him would let out a yell of triumph.

For a few minutes Tom and his friends watched, fascinated. Then they saw Koku slip, while Lamos bent him farther toward the earth. The Indian giant raised his big fist, and Tom saw in it a rock, which the big man was about to bring down on Koku's head.

"Look out, Koku!" yelled Tom.

Tom's giant slid to one side only just in time, for the blow descended, catching him on his muscular shoulder where it only raised a bruise. And then Koku gathered himself for a mighty effort. His face flamed with rage at the unfair trick.

"Bless my bath sponge!" cried Mr. Damon. "This is awful!"

"They must stop!" said Job Titus. "We can't have them fighting like this. It is bad for the others. If it were in fun it would be all right, but they are in deadly earnest. They must stop!"

"Koku, stop!" called Tom. "You must not fight any more!"

"No fight more!" gasped the giant, through his clenched teeth. "This end fight!"

With a mighty effort he broke the hold of Lamos' arms. Then stooping suddenly he seized his rival about the middle, and with a tremendous heave, in which his muscles stood out in great bunches while his very bones seemed to crack, Koku raised Lamos high in the air. Up over his head he raised that mass of muscle, bone and flesh, squirming and wriggling, trying in vain to save itself.

Up and up Koku raised Lamos as the murmur of those watching grew to a shout of amazement and terror. Never had the like been seen in that land for generations. Up and up one giant raised the other. Then calling out something in his native tongue Koku hurled the other from him, clear across the tunnel and up against the opposite rocky wall. The murmuring died to frightened whispers as Lamos fell in a shapeless heap on the floor.

"Ah!" breathed Koku, stretching himself, and extending his brawny arms. "Fight all over, Master."

"Yes, so it seems, Koku," said Tom, solemnly, "but you have killed him. Shame on you!" and he spoke bitterly.

Job Titus had hurried over to the fallen giant.

"He isn't dead," he called, "but I guess he won't wrestle or fight any more. He's badly crippled."

"And him no more try to blow up tunnel, either," said Koku in his hoarse voice. "Me fix: him! No more him take powder, and make tunnel all bust."

"What do you mean, Koku?" asked Tom. "Is that why you fought him? Did he try to wreck the tunnel?"

"So him done, Master. But Koku see--Koku stop. Then um fight."

"Be jabbers an' I wouldn't wonder but what he was right!" cried Tim Sullivan, excitedly. "I did see that beggar." and he pointed to Lamos, who was slowly crawling away, "at the chist where I kape th' powder, but I thought nothin' of it at th' time. What did he try t' do, Koku?"

Then the giant explained in his own language, Tom Swift translating, for Koku spoke English but indifferently well.

"Koku says," rendered Torn, "that he saw Lamos trying to put a big charge of powder up in the place where the balanced rock fits in the secret opening of the tunnel roof. The charge was all ready to fire, and if the giant had set it off he might have brought down the roof of the tunnel and so choked it up that we'd have been months cleaning it out. Koku saw him and stopped him, and then the fight began. We only saw the end."

"Bless my shoe string!" gasped Mr. Damon. "And a terrible end it was. Will Lamos die?"

"I don't think so," answered Job Titus. "But he will be a cripple for life. Not only would he have wrecked the tunnel, but he would have killed many of our men had he set off that blast. Koku saved them, though it seems too bad he had to fight to do it."

An investigation showed that Koku spoke truly. The charge, all ready to set off, was found where he had knocked it from the hand of Lamos. And so Tom's giant saved the day. Lamos was sent back to his own village, a broken and humbled giant. And to this day, in that part of Peru, the great struggle between Koku and Lamos is spoken of with awe where Indians gather about their council fires, and they tell their children of the Titanic fight.

"It was part of the plot," said Job Titus when the usual blast had been set off that day, with not very good results. "This giant was sent to us by our rivals. They wanted him to hamper our work, for they see we have a chance to finish on time. I think that foreman, Serato, is in the plot. He brought Lamos here. We'll fire him!"

This was done, though the Indian protested his innocence. But he could not be trusted.

"We can't take any chances," said Job Titus. "Our time is too nearly up. In fact I'm afraid we won't finish on time as it is. There is too much of that hard rock to cut through."

"There's only one thing to do," said Tom, after an investigation. "As you say, there is more of that hard rock than we calculated on. To try to blast and take it out in the ordinary way will be useless. We must try desperate means."

"What is that?" asked Walter Titus.

"We must set off the biggest blast we can with safety. We'll bore a lot of extra holes, and put in double charges of the explosive. I'll add some ingredients to it that will make it stronger. It's our last chance. Either we'll blow the tunnel all to pieces, or we'll loosen enough rock to make sufficient progress so we can finish on time. What do you say? Shall we take the chance?"

The Titus brothers looked at one another. Failure stared them in the face. Unless they completed the tunnel very soon they would lose all the money they had sunk in it.

"Take the chance!" exclaimed Job. "It's sink or swim anyhow. Set off the big blast, Tom."

"All right. We'll get ready for it as soon as we can."

That day preparations were made for setting off a great charge of the powerful explosive. The work was hurried as fast as was consistent with safety, but even then progress was rather slow. Precautions had to be taken, and the guards about the tunnel were doubled. For it was feared that some word of what was about to be done would reach the rival firm, who might try desperate means to prevent the completion of the work.

There was plenty of the explosive on hand, for Mr. Swift had sent Tom a large shipment. All this while no word had come from Mr. Nestor, and Tom was beginning to think that his prospective father-in-law was very angry with him. Nor had Mary written.

Professor Bumper came and went as he pleased, but his quest was regarded as hopeless now. Tom and his friends had little time for the bald-headed scientist, for they were too much interested in the success of the big blast.

"Well, we'll set her off to-morrow," Tom said one night, after a hard day's work. "The rocky wall is honeycombed with explosive. If all goes well we ought to bring down enough rock to keep the gangs busy night and day."

Everything was in readiness. What would the morrow bring-- success or failure?