"Bless my looking glass, Tom, what does that mean?" exclaimed Mr. Damon. "That face!"

"I don't know," answered the young inventor. "But the sight of some one looking in here seemed to disturb Mr. Titus. We must follow him."

"Perhaps he saw your giant Koku looking in," suggested the odd, little man who blessed everything he could think of. "The sight of his face, to any one not knowing him, Tom, would be enough to cause fright."

"It wasn't Koku who looked in the window," said Tom, decidedly. "It was some stranger. Come on."

The young inventor and Mr. Damon hurried out after the tunnel contractor, who was running down the road that led in front of the Swift homestead.

"He's chasing some one, Tom," called Mr. Damon.

"Yes, I see he is. But who?"

"I can't see any one," reported Mr. Damon, who had run down to the gate, at which his horse was still standing. Mr. Damon had washed the dirt from his hands and face, and was wearing one of Mr. Swift's coats in place of his own split one.

Tom joined the eccentric man and together they looked down the road after the running Mr. Titus. They were in half a mind to join him, when they saw him pull up short, raise his hands as though he had given over the pursuit, and turn back.

"I guess he got away, whoever he was," remarked Tom. "We'll walk down and meet Mr. Titus, and ask him what it all means."

Shortly afterward they came up to the contractor, who was breathing heavily after his run, for he was evidently not used to such exercise.

"I beg your pardon, Tom Swift, for leaving you and Mr. Damon in such a fashion," said Mr. Titus, "but I had to act quickly or lose the chance of catching that rascal. As it was, he got away, but I think I gave him a scare, and h~e knows that I saw him. It will make him more cautious in the future."

"Who was it?" asked Tom.

"Well, I didn't have as close a look as I could have wished for," the contractor said, as he walked back toward the house with Tom and Mr. Damon, "but I'm pretty sure the face that peered in at us through the library window was that of Isaac Waddington."

"And who is he, if it isn't asking information that ought not be given out?" inquired Mr. Damon.

"Oh, no, certainly. I can tell you," said the contractor. "Only perhaps we had better wait until we get back to the house.

"Since one of their men was seen lurking around here there may be others," went on Mr. Titus, when the three were once more seated in the Swift library. "It is best to be on the safe side. The face I saw, I'm sure, was that of Waddington, who is a tool of Blakeson & Grinder, rival tunnel contractors. They put in a bid on this Andes tunnel, but we were lower in our figures by several thousand dollars, and the contract was awarded to us.

"Blakeson & Grinder tried, by every means in their power, to get the job away from us. They even invoked the aid of some Peruvian revolutionists and politicians, but we held our ground and began the work. Since then they have had spies and emissaries on our trail, trying their best to make us fail in our work, so the Peruvian officials might abrogate the contract and give it to them.

"But, so far, we've managed to come out ahead. This Waddington is a sort of spy, and I've found him dodging me several times of late. I suppose he wants to find out my plans so as to be ready to jump in the breach in case we fail."

"Do you think your rivals had anything to do with the difficulties you are now meeting with in digging the tunnel?" asked Mr. Damon. Mr. Titus shook his head.

"The present difficulties are all of Nature's doing," he said. "It's just the abnormally hard rock that is bothering us. Only for that we'd be all right, though we might have petty difficulties because of the mean acts of Blakeson & Grinder. But I don't fear them."

"How do you think this Waddington, if it was he, knew you were coming here?" asked Tom.

"I can only guess. My brother and I have had some correspondence regarding you, Tom Swift. That is, I announced my intention of coming to see you, and my brother wrote me to use my discretion. I wrote back that I would consult you

"Our main office is in New York, where we employ a large clerical and expert force. There is nothing to prevent one of our stenographers, for instance, turning traitor and giving copies of the letters of my brother and myself to our rivals.

"Mind you, I don't say this was done, and I don't suspect any of our employees, but it would be an easy matter for any one to know my plans. I never thought of making a secret of them, or of my trip here. In some way Waddington found out about the last, and he must have followed me here. Then he sneaked up under the window, and tried to hear what we said."

"Do you think he did?" asked Tom.

"I wouldn't be surprised. We took no pains to lower our voices. But, after all, he hasn't learned much that he didn't know before, if he knew I was coming here. He didn't learn the secret of the explosive that must be used, and that is the vital thing. For I defy him, or any other contractor, to blast that hard rock with any known explosive. We've tried every kind on the market and we've failed. We'll have to depend on you, Tom Swift, to help us out with some of your giant cannon powder."

"And I'm not sure that will work," said the young inventor. "I think I'll have to experiment and make a new explosive, if I conclude to go to Peru."

"Oh, you'll go all right!" declared Mr. Titus with a smile. "I can see that you are eager for the adventures I am sure you'll find there, and, besides, your friend here, Mr. Damon, needs you."

"That's what I do, Tom!" exclaimed the odd man. "Bless my excursion ticket, but you must come!"

"I'll have to invent the new powder first," Tom said.

"That's what I like to hear!" exclaimed Mr. Titus. "It shows you are thinking of coming with us."

Tom only smiled.

"I am so anxious to get the proper explosive," Went on Mr. Titus, "that I would even purchase it from our rivals, Blakeson & Grinder, if I thought they had it. But I'm sure they have not, though they may think they can get it.

"That may be the reason they are following me so closely. They may want to know just when we will fail, and have to give up the contract, and they may think they can step in and finish the work. But I don't believe, without your help, Tom Swift, that they can blast that hard rock, and--"

"Well, I'll say this," interrupted Tom, "first come, first served with me, other things being equal. You have applied to me and, like a lawyer, I won't go over to the other side now. I consider myself retained by your firm, Mr. Titus, to invent some sort of explosive, and if I am successful I shall expect to be paid."

"Oh, of course!" cried the contractor eagerly.

"Very good," Tom went on. "You needn't fear that I'll help the other fellows. Now to get down to business. I must see some samples of this rock in order to know what kind of explosive force is needed to rend it."

"I have some in New York," went on the contractor. "I'll have it sent to you at once. I would have brought it, only it is too heavy to carry easily, and I was not sure I could engage you."

"Did that fellow--Waddington, I believe you called him-- get away from you?" asked Mr. Damon.

"Clean away," the contractor answered. "He was a better runner than I."

"It doesn't matter much," Tom said. "He didn't hear anything that would benefit him, and I'll give my men orders to be on the lookout for him. What sort of fellow is he, Mr. Titus?"

The contractor described the eavesdropper, and Mr. Damon exclaimed:

"Bless my turkey wish-bone! I'm sure I passed that chap when I was riding over to see you a while ago, Tom."

"You did?"

"Yes, on the highway. He inquired the way to your place. But there was nothing strange in that, since you employ a number of men, and I thought this one was coming to look for work. I can't say I liked his appearance, though."

"No, he isn't a very prepossessing individual," commented Mr. Titus. "Well, now what's the first thing to be done, Tom Swift?"

"Get me some samples of the rock, so I can begin my experiments."

"I'll do that. And now let us consider about going to Peru. For I'm sure you will be successful in your experiments, and will find for us just the powder or explosive we need."

"We can go together." said Mr. Damon. "I shall certainly feel more at home in that wild country if I know Tom Swift is with me, and I will appreciate the help of you and your friends, Mr. Titus, in straightening out the tangles of our drug business."

"I'll do all I can for you, Mr. Damon."

The three then talked at some length regarding possible plans. Tom sent out word to one of his men to keep a sharp watch around the house and grounds, against the possible return of Waddington, but nothing more was seen of him, at least for the time being.

Mr. Titus drew up a sort of tentative agreement with Tom, binding his firm to pay a large sum in case the young inventor was successful, and then the contractor left, promising to have the rock samples come on later by express.

Mr. Damon, after blessing a few dozen more or less impersonal objects, took his departure, his fractious horse having quieted down in the meanwhile, and Tom was left to himself.

"I wonder what I've let myself in for now," the youth mused, as he went back to his laboratory. "It's a new field for me--tunnel blasting. Well, perhaps something may come of it."

But of the strange adventure that was to follow his agreement to help Mr. Titus, our hero, Tom Swift, had not the least inkling.

Tom went back to his labors over the gyroscope problem, but he could arrive at no satisfactory conclusion, and, tossing aside the papers, covered with intricate figures, he exclaimed:

"Oh, I'm going for a walk! This thing is getting on my nerves."

He strolled through the Shopton streets, and as he reached the outskirts of the town, he saw just ahead of him the figure of a girl. Tom quickened his pace, and presently was beside her.

"Where are you going, Mary?" he asked.

"Oh, Tom! How you startled me!" she exclaimed, turning around. "I was just thinking of you."

"Thanks! Something nice?"

"I shan't tell you!" and she blushed. "But where are you going?"

"Walking with you!"

Tom was nothing if not bold.

"Hadn't you better wait until you're asked?" she retorted, mischievously.

"If I did I might not get an invitation. So I'm going to invite myself, and then I'm going to invite you in here to have an ice cream soda," and he and Miss Nestor were soon seated at a table in a candy shop.

Tom had nearly finished his ice cream when he glanced toward the door, and started at the sight of a man who was entering the place.

"What's the matter?" asked Mary. "Did you drop some ice cream, Tom?"

"No, Mary. But that man--"

Mary turned in time to see an excited man hurry out of the candy shop after a hasty glance at Tom Swift.

"Who was he?" the girl asked.

"I--er--oh, some one I thought I knew, but I guess I don't," said Tom, quickly. "Have some more cream, Mary?"

"No, thank you. Not now."

Tom was glad she did not care for any, as he was anxious to get outside, and have a look at the man, for he thought he had recognized the face as the same that had peered in his window. But when he and Miss Nestor reached the front of the shop the strange man was not in sight.

"I guess he came in to cool off after his run," mused Tom, "but when he saw me he didn't care about it. I wonder if that was Waddington? He's a persistent individual if it was he."

"Are you undertaking any new adventures, Tom?" asked Mary.

"Well, I'm thinking of going to Peru."

"Peru!" she cried. "Oh, what a long way to go! And when you get there will you write to me? I'm collecting stamps, and I haven't any from Peru."

"Is that--er--the only reason you want me to write?" asked Tom.

"No," said Mary softly, as she ran up the walk.

Tom smiled as he turned away.

Three days later he received a box from New York. It contained the samples from the Andes tunnel, and Tom at once began his experiments to discover a suitable explosive for rending the hard stone.

"It is compressed molten lava," said Mr. Swift. "You'll never get an explosive that will successfully blast that, Tom."

"We'll see," declared the young inventor.