Tom Swift, seated in his laboratory engaged in trying to solve a puzzling question that had arisen over one of his inventions, was startled by a loud knock on the door. So emphatic, in fact, was the summons that the door trembled, and Tom started to his feet in some alarm.

"Hello there!" he cried. "Don't break the door, Koku!" and then he laughed. "No one but my giant would knock like that," he said to himself. "He never does seem able to do things gently. But I wonder why he is knocking. I told him to get the engine out of the airship, and Eradicate said he'd be around to answer the telephone and bell. I wonder if anything has happened?

Tom shoved back his chair, pushed aside the mass of papers over which he had been puzzling, and strode to the door. Flinging it open he confronted a veritable giant of a man, nearly eight feet tall, and big in proportion. The giant, Koku, for that was his name, smiled in a good-natured way, reminding one of an overgrown boy.

"Master hear my knock?" the giant asked cheerfully.

"Hear you, Koku? Say, I couldn't hear anything else!" exclaimed Tom. "Did you think you had to arouse the whole neighborhood just to let me know you were at the door? Jove! I thought you'd have it off the hinges."

"If me break, me fix," said Koku, who, from his appearance and from his imperfect command of English, was evidently a foreigner.

"Yes, I know you can fix lots of things, Koku," Tom went on, kindly enough. "But you musn't forget what enormous strength you have. That's the reason I sent you to take the engine out of the airship. You can lift it without using the chain hoist, and I can't get the chain hoist fast unless I remove all the superstructure. I don't want to do that. Did you get the engine out?"

"Not quite. Almost, Master."

"Then why are you here? Has anything gone wrong?"

"No, everything all right, Master. But man come to machine shop and say he must have talk with you. I no let him come past the gate, but I say I come and call you."

"That's right, Koku. Don't let any strangers past the gate. But why didn't Eradicate come and call me. He isn't doing anything, is he? Unless, indeed, he has gone to feed his mule, Boomerang."

"Eradicate, he come to call you, but that black man no good!" and Koku chuckled so heartily that he shook the floor of the office.

"What's the matter with Eradicate?" asked Tom, somewhat anxiously. "I hope you and he haven't had another row?" Eradicate had served Tom and his father long before Koku, the giant, had been brought back from one of the young inventor's many strange trips, and ever since then there had been a jealous rivalry between the twain as to who should best serve Tom.

"No trouble, Master," said Koku. "Eradicate he start to come and tell you strange man want to have talk, but Eradicate he no come fast enough. So I pick him up, and I set him down by gate to stand on guard, and I come to tell you. Koku come quick!"

"Oh, I knew it must be something like that!" exclaimed Tom in some vexation. "Now I'll have Eradicate complaining to me that you mauled him. Picked him up and set him down again;

"Sure. One hand!" boasted the giant. "Eradicate him not be heavy. More as a sack of flour now."

"No, poor Eradicate is getting pretty old and thin," commented Tom. "He can't move very quickly. But you should have let him come, Koku. It makes him feel badly when he thinks he can't be of service to me any more.

"Man say he in hurry." The giant spoke softly, as though he felt the gentle rebuke Tom administered. "Koku run quick tell you--bang on door."

"Yes, you banged all right, Koku. Well, it can't be helped, I reckon. Where is this strange man? Who is he? Did you ever see him before?"

"Me no can tell, Master. Not sure. But him now be at the outer gate. Eradicate watch."

"All right. I'll go and see who it is. I don't want any strangers poking around here, especially With the plans of my new gyroscope lying in plain view."

Before he left the laboratory Tom swept into a desk drawer the mass of papers and blue prints, and locked the receptacle.

"No use taking any chances," he remarked. "I've had too much trouble with people trying to get inside information about dad's and my patents. Now, Koku, I'll go and see this man."

The buildings composing the plant of Tom Swift and his father at Shopton were enclosed by a high, board fence, and at one of the entrances was a sort of gate-house, where some one was always on guard. Only those who could give a good account of themselves, workmen in the plant, or those known to the sentinel were admitted.

It happened that the colored man, Eradicate, was on guard at the gates this day when the stranger asked to see Tom. Koku, working on the airship engine not far away, saw the stranger. Hearing the man say he was in a hurry and noting the slow progress of the aged Eradicate, who was troubled with rheumatism, the giant took matters into his own hands.

Tom Swift entered the gate-house and saw, seated in a chair, a man who was impatiently tapping the floor with his thick-soled shoe.

"Looks like a detective or a policeman in disguise," thought Tom, for, almost invariably, members of this profession wear very thick-soled shoes. Opposite the stranger sat Eradicate, a much-injured look on his honest, black face.

"Oh, Massa Tom!" exclaimed Eradicate, as soon as the young inventor entered. "Dat Koku he--he--he done gone and cotch me by de collar ob mah coat, an' den he lif' me up, an' he sot me down so hard--so hard--dat he jar loose all mah back teef!" and Eradicate opened his mouth wide to display his gleaming ivories.

"Eradicate, he no can come quick. He walk like so fashion!" and Koku, who had followed the young inventor, imitated the limping gait of the colored man with such a queer effect that Tom could not help laughing, and the stranger smiled.

"Ef I gits holt on yo'--ef I does, yo' great, big, overgrown lummox, Ah'll--Ah'll--" began the colored man, stammeringly.

"There. That will do now!" interrupted Tom. "Don't quarrel in here. Koku, get back to that engine and lift out the motor. Eradicate, didn't father tell you to whitewash the chicken coops to-day?"

"Dat's what he done, Massa Tom.

"Well, go and see about that. I'll stay here for a while, and when I leave I'll call one of you, or some one else, to be on guard. Skip now!"

Having thus disposed of the warring factions, Tom turned to the stranger and after apologizing for the little interruption, asked:

"You wished to see me?"

"If you're Tom Swift; yes."

"Well, I'm Tom Swift," and the young owner of the name smiled.

"I hope you will pardon a stranger for calling on you," resumed the man, "but I'm in a lot of trouble, and I think you are the only one who can help me out."

"What sort of trouble?" Tom inquired.

"Contracting trouble--tunnel blasting, to be exact. But if you have a few minutes to spare perhaps you will listen to my story. You will then be better able to understand my difficulty."

Tom Swift considered a moment. He was used to having appeals for help made to him, and usually they were of a begging nature. He was often asked for money to help some struggling inventor complete his machine.

In many cases the machines would have been of absolutely no use if perfected. In other cases the inventions were of the utterly hopeless class, incapable of perfection, like some perpetual motion apparatus. In these cases Tom turned a deaf ear, though if the inventor were in want our hero relieved him.

But this case did not seem to be like anything Tom had ever met with before.

"Contracting trouble--blasting," repeated the youth, as he mused over what he had heard.

"That's it," the man went on. "Permit me to introduce myself" and he held out a card, on which was the name

MR. JOB TITUS

Down in the lower left-hand corner was a line:

"Titus Brothers, Contractors."

"I am glad to meet you, "Mr. Titus," Tom said warmly, offering his hand. "I don't know anything about the contracting business, but if you do blasting I suppose you use explosives, and I know a little about them."

"So I have heard, and that's why I came to you," the contractor went on. "Now if you'll give me a few minutes of your time--"

"You had better come up to the house," interrupted Tom. "We can talk more quietly there."

Calling a young fellow who was at work near by to occupy the gate-house, Tom led Mr. Titus toward the Swift homestead, and, a little later, ushered him into the library.

"Now I'll listen to you," the youth said, "though I can't promise to aid you."

"I realize that," returned Mr. Titus. "This is a sort of last chance I'm taking. My brother and I have heard a lot about you, and when he wrote to me that he was unable to proceed with his contract of tunneling the Andes Mountains for the Peruvian government, I made up my mind you were the one who could help us if you would."

"Tunneling the Andes Mountains!" exclaimed Tom.

"Yes. The firm represented by my brother and myself have a contract to build a railroad for the Peruvian government. At a point some distance back in the district east of Lima, Peru, we are making a tunnel under the mountain. That is, we have it started, but now we can't advance any further."

"Why not?"

"Because of the peculiar character of the rock, which seems to defy the strongest explosive we can get. Now I understand you used a powder in your giant cannon that--"

Mr. Titus paused in his explanation, for at that moment there arose such a clatter out on the front piazza as effectually to drown conversation. There was a noise of the hoofs of a horse, the fall of a heavy body, a tattoo on the porch floor and then came an excited shout:

"Whoa there! Whoa! Stop! Look out where you're kicking! Bless my saddle blanket! Ouch! There I go!"