Tom Swift acted promptly, for he realized the necessity. The events that had hedged him about since he had begun work on his giant cannon made him suspicious. He did not quite know whom to suspect, nor the reasons for their actions, but he had been on the alert for several days, and was now ready to act.

The instant Ned answered as he did, and warned Tom, the young inventor slid his hand under his pillow and pressed an auxiliary electric switch he had concealed there. In a moment the rooms were flooded with a bright light, and the two lads had a momentary glimpse of an intruder making a dive for the window.

"There he is, Tom!" cried Ned.

"What do you want?" demanded Tom, instinctively. But the intruder did not stay to answer.

Instead, he made a dive for the casement. It was one story above the ground, but this did not cause him any hesitation. It was summer, and the window was open, though a wire mosquito net barred the aperture. This was no hindrance to the man, however.

As Ned and Tom leaped from their beds, Ned catching up the heavy, empty water pitcher as a weapon, and Tom an old Indian war club that served as one of the ornaments of his room, the fellow, with one kick, burst the screen.

Then, clambering out on the sill, he dropped from sight, the boys hearing him land with a thud on the turf below. It was no great leap, though the fall must have jarred him considerably, for the boys heard him grunt, and then groan as if in pain.

"Quick!" cried Ned. "Ring the bell for Koku, Ned. I want to capture this fellow if possible."

"Who is he?" asked Ned.

"I don't know, but we'll see if we can size him up. Signal for the giant!"

There was an electric bell from Tom's room to the apartment of his big servant, and a speaking tube as well. While Ned was pressing the button, and hastily telling the giant what had happened, urging him to get in pursuit of the intruder, Tom had taken from his bureau a powerful, portable, electric flash lamp, of the same variety as that used by the would-be thief. Only Tom's was provided with a tungsten filament, which gave a glaring white pencil of light, increased by reflectors.

And in this glare the young inventor saw, speeding away over the lawn, the form of a big man.

"There he goes, Ned!" he shouted.

"So I see. Koku will be right on the job. I told him not to dress. Can you make out who the fellow is?"

"No, his back is toward us. But he's limping, all right. I guess that jump jarred him up a bit. Where is Koku?"

"There he goes now!" exclaimed Ned, as a figure leaped from the side door of the house--a gigantic figure, scantily clad.

"Get to him, Koku!" cried Tom.

"Me git, Master!" was the reply, and the giant sped on.

"Let's go out and lend a hand!" suggested Ned, looking at the water pitcher as though wondering what he had intended to do with it.

"I'm with you," agreed Tom. "Only I want to get into something a little more substantial than my pajamas."

As the two lads hurriedly slipped on some clothing they heard the voice of Mr. Swift calling:

"What is it, Tom? Has anything happened?"

"Nothing much," was the reassuring answer. "It was a near- happening, only Ned woke up in time. Someone was in our rooms--a burglar, I guess."

"A burglar! Good land a massy!" cried Eradicate, who had also gotten up to see what the excitement was about. "Did you cotch him, Massa Tom?"

"No, Rad; but Koku is after him."

"Koku? Huh, he nebber cotch anybody. I'se got t' git out dere mahse'f! Koku? Hu! I s'pects it's dat no-'count cousin ob mine, arter mah chickens ag'in! I'll lambaste dat coon when I gits him, so I will. I'll cotch him for yo'-all, Massa Tom," and, muttering to himself, the aged colored man endeavored to assume the activity of former years.

"Hark!" exclaimed Ned, as he and Tom were about ready to take part in the chase. "What's that noise, Tom?"

"Sounds like a motor-cycle."

"It is. That fellow--"

"It's the same chap!" interrupted Tom. "No use trying to chase him on that speedy machine. He's a mile away from here by now. He must have had it in waiting, ready for use. But come on, anyhow."

"Where are you going?"

"Out to the shop. I want to see if he got in there."

"But the charged wires?"

"He may have cut them. Come on."

It was as Tom had suspected. The deadly, charged wires, that formed a protecting cordon about his shops, had been cut, and that by an experienced hand, probably by someone wearing rubber gloves, who must have come prepared for that very purpose. During the night the current was supplied to the wires from a storage battery, through an intensifying coil, so that the charge was only a little less deadly than when coming direct from a dynamo.

"This looks bad, Tom," said Ned.

"It does, but wait until we get inside and look around. I'm glad I took my gun-plans to the house with me."

But a quick survey of the shop did not reveal any damage done, nor had anything been taken, as far as Tom could tell. The office of his main shop was pretty well upset, and it looked as though the intruder had made a search for something, and, not finding it, had entered the house.

"It was the gun-plans he was after, all right," decided Tom. "And I believe it was the same fellow who has been making trouble for me right along."

"You mean General Waller?"

"No, that German--the one who was at the machine shop."

"But who is he--what is his object?"

"I don't know who he is, but he evidently wants my plans. Probably he's a disappointed inventor, who has been trying to make a gun himself, and can't. He wants some of my ideas, but he isn't going to get them. Well, we may as well get back to bed, after I connect these wires again. I must think up a plan to conceal them, so they can't be cut."

While Tom and Ned were engaged on this, Koku came back, much out of breath, to report:

"Me not git, Master. He git on bang-bang machine and go off-- puff!"

"So we heard, Koku. Never mind, we'll get him yet."

"Hu! Ef I had de fust chanst at him, I'd a cotched dat coon suab!" declared Eradicate, following the giant. "Koku he done git in mah way!" and he glared indignantly at the big man.

"That's all right, Rad," consoled Tom. "You did your best. Now we'll all get to bed. I don't believe he'll come back." Nor did he.

Tom and Ned were up at the first sign of daylight, for they wanted to go to the steel works, some miles away, in time to see the cannon taken out of the mould, and preparations made for boring the rifle channels. They found the manager, anxiously waiting for them.

"Some of my men are as interested in this as you are," he said to the young inventor. "A number of them declare that the cast will be a failure, while some think it will be a success."

"I think it will be all right, if my plans were followed," said Tom. "However, we'll see. By the way, what became of that German who made such a disturbance the day we cast the core?"

"Oh, you mean Baudermann?"

"Yes."

"Why, it's rather queer about him. The foreman of the shop where he was detailed, saw that he was an experienced man, in spite of his seemingly stupid ways, and he was going to promote him, only he never came back."

"Never came back? What do you mean?"

"I mean the day after the cast of the gun was made he disappeared, and never came back."

"Oh!" exclaimed Tom. He said nothing more, but he believed that he understood the man's actions. Failing to obtain the desired information, or perhaps failing to spoil the cast, he realized that his chances were at an end for the present.

With great care the gun was hoisted from the mould. More eyes than Tom's anxiously regarded it as it came up out of the casting pit.

"Bless my buttonhook!" cried Mr. Damon, who had gone with the lads. "It's a monster; isn't it?"

"Oh, wait until you see it with the jackets on exclaimed Ned, who had viewed the completed drawings. "Then you'll open your eyes."

The great piece of hollow steel tubing was lifted to the boring lathe. Then Tom and the manager examined it for superficial flaws.

"Not one!" cried the manager in delight.

"Not that I can see," added Tom.. "It's a success--so far."

"And that was the hardest part of the work," went on the manager of the steel plant. "I can almost guarantee you success from now on."

And, as far as the rifling was concerned, this was true. I will not weary you with the details of how the great core of Tom Swift's giant cannon was bored. Sufficient to say that, after some annoying delays, caused by breaks in the machinery, which had never before been used on such a gigantic piece of work, the rifling was done. After the jackets had been shrunk on, it would be rifled again, to make it true in case of any shrinkage.

Then came the almost Herculean task of shrinking on the great red-hot steel jackets and wire-windings, that would add strength to the great cannon. To do this the central core was set up on end, and the jackets, having been heated in an immense furnace, were hoisted by a great crane over the core, and lowered on it as one would lower his napkin ring over the rolled up napkin.

It took weeks of hard work to do this, and Tom and Ned, with Mr. Damon occasionally for company, remained almost constantly at the plant. But finally the cannon was completed, the rifling was done over again to correct any imperfections, and the manager said:

"You cannon is completed, Mr. Swift. I want to congratulate you on it. Never have we done such a stupendous piece of work. Only for your plans we could not have finished it. It was too big a problem for us. Your cannon is completed, but, of course, it will have to be mounted. What about the carriage?"

"I have plans for that," replied Tom; "but for the present I am going to put it on a temporary one. I want to test the gun now. It looks all right, but whether it will shoot accurately, and for a greater distance than any cannon has ever sent a projectile before, is yet to be seen."

"Where will you test it?"

"That is what we must decide. I don't want to take it too far from here. Perhaps you can select a place where it would be safe to fire it, say with a range of about thirty miles."

"Thirty miles! why, my dear sir--"

"Oh, I'm not altogether sure that it will go that distance," interrupted Tom, with a smile; "but I'm going to try for it, and I want to be on the safe side. Is there such a place near here?"

"Yes, I guess we can pick one out. I'll let you know."

"Then I must get back and arrange for my powder supply," went on the young inventor. "We'll soon test my giant cannon!"

"Bless my ear-drums!" cried Mr. Damon. "I hope nothing bursts. For if that goes up, Tom Swift--"

"I'm not making it to burst," put in Tom, with a smile. "Don't worry. Now, Ned, back to Shopton to get ready for the test."