"Bless my buttons!" cried Mr. Damon.

"Let's chase after him!" yelled Ned.

"Koku kin run de fastest oh any oh us," put in Eradicate. "Let him go."

"Hold on--wait a minute!" exclaimed Tom. "We want to know who that man is--and why we're going to chase after him. Koku, I guess it's up to you. Something has been going on here that I don't know anything about. Explain!"

"Well, it's no use to chase after him now," said Ned. "There he goes on his motor-cycle."

As he spoke the man, who, even from a rear view, presented all the characteristics of an army man, so straight was his carriage, leaped upon a motor-cycle that he pulled from the roadside bushes, and soon disappeared in a cloud of dust.

"No, he's gone," spoke Tom, half-regretfully. "But who was he, Koku? You seemed to know him. What was he doing out here, watching my test?"

"Me tell," said the giant, simply. "Little while after Master come back from where him say big gun all go smash, man come to shop when Master out one day. Him very nice man, and him say him know you, and want to help you make big cannon. I say, 'Master no be at home.' Man say him want to give master a little present of powder for use in new cannon. Master be much pleased, man say. Make powder better. I take, and I want Master to be pleased. I put stuff what man gave me in new powder. Man go away--he laugh-- he say he be here today see what happen --I tell him you go to make test today. Man say Master be much surprised. That all I know."

Silence followed Koku's statement. To Ned and Mr. Damon it was not exactly clear, but Tom better understood his giant servant's queer talk.

"Is that what you mean, Koku?" asked the young inventor, after a pause. "Did some stranger come here one day when I was out, after I had made my new powder, and did he give you some 'dope' to put in it?"

"What you mean by 'dope'?"

"I mean any sort of stuff."

"Yes, man give me something like sugar, and I sprinkle it on new powder for to surprise Master."

"Well, you've done it, all right," said Tom, grimly. "Have you any of the stuff left?"

"I put all in iron box where Master keep new powder."

"Well, then some of it must be there yet. Probably it sifted through the excelsior-like grains of my new explosive, and we'll find it on the bottom of the powder-case. But enough stuck to the strands to spoil my test. I'll just take a reading of the gauges, and then we'll make an investigation."

Tom, with Ned to help him, made notes of how far the weight had risen in the tube, and took data of other points in the experiment.

"Pshaw!" exclaimed Tom. "There wasn't much more force to my new powder, doped as it apparently has been, than to the stuff I can buy in the open market. But I'm glad I know what the trouble is, for I can remedy it. Come on back to the shop. Koku, don't you ever do anything like this again," and Tom spoke severely.

"No, Master," answered the giant, humbly.

"Did you ever see this man before, Koku?"

"No, Master."

"What kind of a fellow was he?" asked Ned.

"Oh, him got whiskers on him face, and stand very straight, like stick bending backwards. Him look like a soldier, and him blink one eye more than the other."

Tom and Ned started and looked at one another.

"That description fits General Waller," said Ned, in a low voice to his chum.

"Yes, in a way; but it would be out of the question for the General to do such a thing. Besides, the man who ran away, and escaped on his motor-cycle, was larger than General Waller."

"It was hard to tell just what size he was at the distance," spoke Ned. "It doesn't seem as though he would try to spoil your experiments. though."

"Maybe he hoped to spoil my cannon," remarked Tom, with a laugh that had no mirth in it. "My cannon that isn't cast yet. He probably misunderstood Koku's story of the test, and had no idea it was only a miniature, experimental, gun.

"This will have to be looked into. I can't have strangers prowling about here, now that I am going to get to work on a new invention. Koku, I expect you, after this, not to let strangers approach unless I give the word. Eradicate, the same thing applies to you. You didn't see anything of this mysterious man; did you?"

"No, Massa 'Tom. De only s'picious man I see was mab own cousin sneakin' around mah chicken coop de odder night. I tooks mah ole shot gun, an' sa'ntered out dat way. Den in a little while dere wasn't no s'picious man any mo'."

"You didn't shoot him; did you, Rad?" cried Tom, quickly.

"No, Massa Tom--dat is, I didn't shoot on puppose laik. De gun jest natchelly went off by itself accidental-laik, an' it peppered him good an' proper."

"Why, Rad!" cried Ned. "You didn't tell us about this."

"Well, I were 'shamed ob mah cousin, so I was. Anyhow, I only had salt an' pepper in de gun--'stid ob shot. I 'spect mah cousin am pretty well seasoned now. But dat's de only s'picious folks I see, 'ceptin' maybe a peddler what wanted t' gib me a dish pan fo' a pair ob ole shoes; only I didn't hab any."

"There are altogether too many strangers coming about here," went on Tom. "It must be stopped, if I have to string charged electric wires about the shops as I once did."

They hurried back to the shop where the new powder was kept, and Tom at once investigated it. Taking the steel box from where it was stored he carefully removed the several handfuls of excelsior-like explosive. On the bottom of the box, and with some of it clinging to some of the powder threads, was a sort of white powder. It had a peculiar odor.

"Ha!" cried Tom, as soon as he saw it. "I know what that is. It's a new form of gun-cotton, very powerful. Whoever gave it to Koku to put on my powder hoped to blow to atoms any cannon in which it might be used. There's enough here to do a lot of damage."

"How is it that it didn't blow your test cylinder to bits?" asked Ned.

"For the reason that the stuff I use in my powder and this new gun-cotton neutralized one another," the young inventor explained. "One weakened the other, instead of making a stronger combination. A chemical change took place, and lucky for us it did. It was just like a man taking an over-dose of poison--it defeated itself. That's why my experiment was a failure. Now to put this stuff where it can do no harm. Is this what that man gave you, Koku?"

"That's it, Master."

There came a tap on the door of the private room, and instinctively everyone started. Then came the voice of Eradicate, saying:

"Dere's a army gen'men out here to see you. Massa Tom; but I ain't gwine t' let him in lessen as how you says so."

"An army gentleman!" repeated Tom.

"Yais, sah! He say he General Waller, an' he come on a motor- cycle."

"General Waller!" exclaimed Tom. "What can he want out here?"

"And on a motor-cycle, too!" added Ned. "Tom, what's going on, anyhow?"

The young inventor shook his head.

"I don't know," he replied; "but I suppose I had better see him. Here. Koku, put this powder away, and then go outside. Mr. Damon, you'll stay; won't you?"

"If you need me, Tom. Bless my finger nails! But there seems to be something wrong here."

"Show him in, Rad!" called Tom.

"Massa Gen'l Herodotus Waller!" exclaimed the colored man in pompous tones, as he opened the door for the officer, clad in khaki, whom Tom had last seen at Sandy Hook.

"Ah, how do you do, Mr. Swift!" exclaimed General Waller, extending his hand. "I got your letter inviting me to a test of your new explosive. I hope I am not too late."

Tom stared at him in amazement.