won his own way and had helped to make famous the output of the Interstate Aero Company, of which Mr. Brackett was practically the owner. Still, Dave felt that all he had gained had been through the encouragement and assistance of the manufacturer. As a matter of fact, Dave deferred greatly to the opinion and direction of this valuable friend. He had been expecting his arrival daily at the Midlothian grounds, to talk over the situation and prospects for future work.

“Whew!” ejaculated Hiram, as he pulled open the door of the hangar, and rushed in. “Fire!”

“No, only smoke,” corrected Dave—“and not much of that, lucky for us!”

“I say!” cried his companion in an exasperated tone as he went spinning off his feet. Contact with an indistinct, wildly-rushing human form had caused this. There had been a smoky haze inside the hangar that had hid the aroused sleeper from clear view. Now, however, the tramp was plainly visible. He looked startled and scared and he was nursing the fingers of his left hand in the palm of the other.

“What’s happened—are you hurt?” inquired Dave.

“Whew! Well—why, oh, it’s only a little burn, but—catch the rascal!”

As the speaker finished the rapidly shouted sentence he dashed towards the fence. Upon this the rear of the hangar backed. The tramp was quick, and as nimble as a monkey as he ran at the fourteen-foot barrier. One of its slanting supports carried him within reach of the bracing stringer. He lifted himself to this. From the ground the aeroplane boys could see him bobbing his head about among the barbed wire runners, strung along on top of the fence, as if to catch a view of a vacant field beyond.

The tramp yelled out some disjointed words, and shook his fist angrily, as if after a scurrying fugitive. Then he slid down to the ground and faced Dave and Hiram, panting and excited.

“He made off—he got away!” the tramp ejaculated. “Too bad! I’m so big I couldn’t get through that window.”

“What window?” inquired Hiram.

“Cut in the fence that makes the rear of the hangar,” was explained. “Come in. Let me show you.”

Dave cast a hurried glance about the interior of the hangar as he entered it. Except that the little door which protected the rear window opening was out of place, everything seemed in order. Their tramp friend, however, had stooped over near the Ariel.

“Look here,” he said, and the boys, crowding nearer to him, noticed that he held in his hand the crisped, blackened end of what resembled a fuse.

“Where does it lead to?” asked the startled Hiram.

Very gingerly the tramp ran eye and hand along the sinister-looking fuse. He seemed to locate its end as he reached under a corner of the airplane.

“Better get it outside,” he suggested, and the boys saw that he had unearthed a round box-like object resembling a dry electric battery. The fuse ran to its center. The tramp carried it outside, set it down in the grass at a safe distance from the hangar, and observed:

“Better soak it in a pail of water before you handle it much. Those things are dangerous; very much so! If I don’t mistake, you’ll find it’s dynamite.”

“Then some one’s up to a mean trick again!” cried the excitable Hiram, unable to repress himself. “Dave, you’re not going to stand this; are you?”

“Why, Hiram,” responded Dave quietly, “we don’t yet know our bearings. Maybe it’s a joke——”

“Joke! Joke!” fairly yelled Hiram. “Yes, the same kind of a joke as that fellow Vernon played on us when he stole the Comet at the Washington aero meet. Or like that partner of his, who dropped a steel hook on the biplane purposely to wreck us.”

Hiram had named the enemy the boys, according to past experience, had most to fear. Dave, however, was not wont to jump at hasty conclusions. He did not do so in the present instance. He put aside unproven suspicion for the time being.

“We had better make an investigation, and find out all we can,” Dave suggested. “You said your name was Borden, I believe?” he observed to the tramp.

“That’s it—Roving Borden, they call me. I was Henry, in my respectable days.”

“Very good, Mr. Borden, now please tell us what you know of this affair,” Dave requested.

“I’m a pretty sound sleeper,” narrated the tramp, “especially in such a famous bunk as you kindly gave me. I’d slept so long, though, that I fancy I was more easily awakened than usual. What I saw was done quickly. Some one must have forced in that shutter yonder. He had just put that thing we discovered under the edge of the balloon. The end of the fuse was spluttering as I woke up. I saw the fellow bolt through the window. Then I sprang up and grabbed the fuse. As I snapped it in two, it sort of exploded. See where it burned me?” and the speaker showed his blackened fingers.

“Lucky for us you were on hand!” broke in Hiram.

“I believe this to be the work of an enemy,” spoke Dave, rather solemnly, after a moment’s deliberation. “Did you have a good look at the fellow you saw go through the window, Mr. Borden?”

“I should say, I did!” exclaimed the tramp. “When a fellow gets waked up suddenly and startled, like I was, everything hits his brain as if it were a photograph camera. Say,” and the speaker half closed his eyes, “I can see that rascal just as plain as day now. By the way, too, if I’m not mistaken I saw the very same individual hanging around the outside of the grounds when I sneaked in last night.”

“Dave, I call this serious!” cried Hiram, aroused and indignant. “It’s a queer thing if we can’t have protection from the cowards who steal in on us when we’re not watching, and try to wreck our aircraft! I’ll wager the stuff in that canister would blow a small mountain to pieces!”

“Guess I’d have gone up, too, if it was that bad,” remarked the tramp with a shiver.

Dave went to the window and examined it. The edges of the solid board shutter showed the marks of some chisel, or other tool, used to pry it open. Then the chums went outside. On the way Dave caught up a bundle of waste used in removing oil and grime from the machinery of the air crafts, and a newspaper.

The others watched him in silence as he carefully wound up what was left of the fuse, and placed it and the canister, to which it was attached, in the waste then, wrapping all in the newspaper, he said to Hiram:

“I’m going down to the manager’s office.”

“Going to find out if that’s a real explosive; aren’t you?” inquired Hiram.

“Yes, that’s my purpose. If we find that it is, we can make up our minds that the people we have had trouble with before are still on our trail. I fancied we’d beaten them off so many times they had now gotten sick of such doings.”

“Oh, if it’s Vernon, or any of his crowd, they’re the kind that will keep on pestering us to the last,” declared Hiram. “Be back soon, Dave. I’m all rattled, and anxious.”

The young birdman proceeded on his way. Hiram turned to the tramp, who had manifested a decided interest in all