Nothing else happened that night, but the boys had already had enough excitement to keep them awake long past their usual time for turning in. Some of them, indeed, were for starting out in pursuit of the Big Four, but Mr. Fulton promptly squelched the plan. There was little hope of finding the boat in the dense darkness.

Next morning, before breakfast, Sid Walmaly and Dave were sent out on a scouting expedition, but they were not gone long. The Big Four had been found, barely half a mile down, stranded on a sand-bar. A jagged hole in the side showed where the kidnappers had tried to scuttle the craft.

After this event, the boys settled to their work in high spirits, undeterred by the fact that the motor was still missing, although Mr. Fulton felt sure it could not have been taken from the island. Phil ventured to advance a theory, which the boys were inclined to scout but which Mr. Fulton finally decided was at least worth the time and effort it would take to try it out.

The men had had no time to carry the motor far, argued Phil. They had not gone to their boat, else they could hardly have made their way back to the hangar. They might of course have picked it up after they had been frightened away, but there had been hardly time for that. They had undoubtedly hidden it in the first place. The easiest place to hide the thing was in the river, and the closest trail to the river hit the extreme north end, where there was a steep-sided bay.

"Who's the best swimmer in the crowd?" asked Mr. Fulton. "I don't dare take very many away from the job, but we've got to have the motor."

"Jerry Ring's the best swimmer and diver in Watertown," announced Dave without hesitation. Mr. Fulton turned inquiringly to the Boy Scouts, but no one answered his questioning look until Phil at last spoke up quietly:

"I'll go along if you need another one."

"I do. You two take the Scout boat and bring her around the point. I'll go through the woods—be there in half an hour or so, when I get things running smoothly here. Be careful you don't find the gas-eater before I get there," he jested.

But it was more than half an hour before Mr. Fulton came upon the two boys, stripped to their B-V-D's and at that instant resting on the bank. He came up just in time to hear Jerry say: "I used to think I could dive! Where'd you get onto it?"

"Just Scout stuff," laughed Phil, modestly. "Every Scout in the patrol's got swimming and diving honors."

"Good!" broke in Mr. Fulton. "Dive me up that motor and I'll get you a special honor as a substitute submarine."

"We've worked down from the point, scraping bottom for twenty feet out—that's about as far as they could heave it, we figured. We've just got to the place where I'd have dived first-off if I had only one chance at it. Here goes for that leather medal," as Phil rose and poised himself for the plunge.

It was as pretty a dive as one could want to see. He split the water with a clean slash, with hardly a bubble. A minute, another, and another passed, the two on shore watching the surface expectantly. They began to grow worried.

"He's been beating me right along" confessed Jerry. "I can't come within a full minute of his ordinary dives. This one is a pippin—there he blows!"

Spouting like a young whale, Phil broke the water and came ashore in long reaching strokes.

"I tried my best!" he gasped as he pushed back his hair and rubbed the water from his eyes. "But I couldn't make it!"

"Better luck next time," encouraged Mr. Fulton. "If you don't find her in two more dives like that, why she isn't in Plum Run, that's all!"

"Find her? I was talking about lifting her. Guess we'll have to get a rope on her—she's pretty well down in the mud."

"Hurray!" shouted Jerry, giving his chum a sounding smack on the wet back. "Man the lifeboats! I chucked a rope in the bow of the boat."

Mr. Fulton stood on the bank to mark the line, while the boys pushed the boat out to where Phil had come up, some twenty feet from shore. Jerry slipped over the side, one end of the rope in his hand. He did not remain long below.

Clambering in at the stern, he shouted: "Hoist away—she's hooked!"

And there was the motor, clogged with mud, to be sure, but undamaged. Mr. Fulton stepped into the boat and they rowed quickly back to the "dock." While the two boys put on their clothes over their wet underwear, he hurried back to the workshop to see how things were going. A few minutes later they followed with the motor.

They felt, after this fortunate end of the adventure, that Mr. Fulton ought once more to be his own cheery self, but a look of gloom seemed to have settled down over his face, and his face looked haggard except when he was talking to one of the boys. Jerry finally decided to try to cheer him up.

"Luck was sure breaking our way this morning, wasn't it?" he exclaimed cheerfully as the man came up to where Jerry sat, removing the mud from their prize.

"Fine—fine," agreed Mr. Fulton, but without spirit.

"What's the trouble?" demanded Jerry, sympathetically. "Anything else gone wrong?"

"No—Oh, no."

"You look like the ghost of Mike Clancy's goat. Remember how you always used to be telling Tod and me to grin hardest when we were getting licked worst?"

"I sure ought to grin now, then."

"We're not licked—not by a long shot!"

"Yes we are—by about twenty-four hours. While you were gone I got word from the blacksmith. He says he can't possibly have that propeller shaft we found was snapped, welded before to-morrow afternoon late. Not if we're to have the other things he promised. He's lost his helper—quit him cold."

"No!" exclaimed Jerry, his heart sinking at least two feet. Then, with sudden suspicion, "Do you suppose——"

"I know it," interrupted Mr. Fulton. "Our two friends are working every scheme they know. Blocking our blacksmithing was one of their easiest weapons. I'm only surprised they didn't do it before."

"What can we do?"

"Submit gracefully. But I just can't face those two doubters. First they were so enthusiastic and then so suspicious, that I can't be satisfied unless I convince them. But the stuff's all off—and I told Lewis and Harris to come out to-morrow afternoon at three-thirty to see the Skyrocket make good all my claims!"

"Can't you beg off and get a little more time?"

"They'd be willing enough, I suppose. They don't seem to be in the slightest hurry. But there's that second option that begins operations after to-morrow. No, there's no loophole. All we can do is just peg ahead, and if the blacksmith comes through sooner than he expects, we may have a bare chance. I just sent Tod in to lend a hand."

The blacksmith did do better than his word, for Tod came back late in the afternoon bearing the mended shaft and two smaller parts that were urgently needed.

It took all the rest of that afternoon to lay the shaft in its ball-bearings and true it up. The propeller was still to be attached, but Mr. Fulton declared he would take no chances with that or with the final adjustments in the half light of the growing dusk.

The boys were glad to knock off. They had been working at high tension for a long while now and were beginning to feel the strain. They were all frankly sleepy, too, after the excitement of the night before. As a final precaution against a repetition of the surprise attack they all slept in the hangar, finding the hard floor an unwelcome change from their leafy beds in camp.

But the night passed quietly. With daybreak they were all astir, but the time before breakfast was spent in an invigorating swim in the Plum. Elizabeth had done herself proud in the way of pancakes this last morning, and the boys did full justice. It was almost eight o'clock before anyone returned to the hangar with any intention of working. After barely half an hour there, chiefly spent in polishing and tightening up nuts and draw-buckles, Mr. Fulton drove them all outdoors. "Chase off and play," he insisted. "Tod and I will give her the finishing touches; then you can all come back and help us push her out into the sunlight for the final inspection."

But Elizabeth called them before Mr. Fulton was ready for their services. Heaping platters of beautifully browned perch testified both to her skill and that of the boys.

"Lunch time already?" exclaimed Mr. Fulton in surprise. "Where's the morning gone to?" But he showed that if he hadn't noted the passage of time, his stomach had. As he watched the brown pile diminish under Mr. Fulton's vigorous attack, Phil threatened to go back to the river and start fishing again. "You oughtn't to be eating fish," he joked. "Birds are more your style. Better let me go out and shoot you a duck—or a sparrow; they're more in season."

But Mr. Fulton was at last satisfied, as were all the boys. He sauntered back at once to the hangar. "Guess you chaps can give me a shoulder now, and we'll take her out to daylight. After that you keep out of the way till the show starts—about four o'clock. All but two of you, that is. There's a bearing to grind on the lathe, and a couple of sets of threads to recut."

Tod could not have been driven away, so Jerry volunteered to be the other helper. The whole troop made easy work of running out the Skyrocket. After standing about admiringly a while, they all scattered, some of them, Jerry learned from their conversation, to try to teach Elizabeth how to catch bass. Jerry grinned to himself at this; he had heard Tod tell of the exploits of this slip of a girl, and no boy in camp could do more with a four-ounce bass rod than she could.

Tod and Jerry went at once at their grinding, and by two o'clock all was in readiness. Every rod and strut and bolt and screw was in place, tight as a drum. The nickel and brass of the bearings flashed in the sun; the Skyrocket looked fit as a fiddle. There was still a little gasoline in the gallon can that they had been using for testing the motor, and Tod let it gurgle into the gasoline tank that curved back on the framework just above the pilot's seat.

"Try her out, dad," he urged.

"I'll try the motor," agreed Mr. Fulton, "but I'm not going up until there's somebody around to watch her go through her paces. I've got my shoulder out of splints to-day, but I don't dare use it when there's any danger of strain. Think you're going to have the nerve to go up with me, son?"

Jerry opened his eyes wide. This was the first he had heard of any such plan as that.

"Think I'm going to let you go up alone, with a twisted wing that might give out?" demanded Tod scornfully. "Huh! I'll take her up alone if you'll let me."

"I'll let you fill her up with gas, if you're so ambitious as all that. I see an automobile throwing up the dust on the last hill of the town road. I expect it's our friends. I'll let one of the boys row me across to meet them. Ask Billings, if you can't find the wrench to unscrew the cap of the gasoline reservoir."

Billings proved to be sound asleep, napping off the effects of over-indulgence in browned perch, so the boys decided to await the return of Mr. Fulton, a search of the workshop having failed to reveal the wrench, and none of the Stillsons being big enough to take the big nut that capped the fifty-gallon tank sunk in the ground on the shady north side of the hangar. So they sat down beside it and waited for Mr. Fulton to come back with his visitors.

They finally appeared, Lewis and Harris standing about and listening in unenthusiastic silence as Mr. Fulton glowingly explained the whyness of the various devices and improvements that made the Skyrocket a real invention. They did not even venture an occasional question, although it was easy to see that they were impressed.

"What are they made of? Wood?" exclaimed Jerry in fierce impatience. "Do you know—if it wasn't that we've simply got to beat out those other fellows, I'd almost like to see these two sleepies get left. I don't like them a little bit!"

"Huh! Ask me if I do. They give me the willies. Never did like them, and ever since they acted so nasty about that accident I just plumb hate 'em. You'd think dad was trying to sandbag them or something like that. Just listen to them grouching around. I'd hate to be a woman and married to one of them and have dinner late."

Jerry had seated himself on the top of the reservoir, the cap between his legs. He caught hold of it with his two hands. "It's too blamed bad your dad couldn't hitch up with Uncle Sam!" he exclaimed.

"Yes, and if you believe what the papers say, we're going to need it, too. We might be mixed up in the big war any day."

"Well, I expect we'd better not sit here gassing any longer. Tod, chase over and ask your dad where that wrench is—unless you've got a notion I can twist this thing off with my hands." He gave a playful tug as if to carry out his boast.

"Say!" he cried, "what do you know about this!"

"About what?" asked Tod lazily, a dozen feet away on the way to his father.

"This," answered Jerry, giving the big cap a twirl with his forefinger.
"Some careful of your gasoline you people are!" The cap was loose.

"Something funny about that," declared Tod, coming back. "I saw
Billings screw that on last time myself—with the wrench."

There was something decidedly funny about it, as it turned out. At Tod's alarmed call Mr. Fulton came on the run. "It's been tampered with," was his immediate decision. "Screw on the pump, boys, and force up a gallon or so, If there isn't water in that gas we're the luckiest folks alive. I might have known those crooks had a final shot in their locker!"

"What's the idea?" asked Mr. Harris, with the first interest he had showed.

"Somebody's trying to block the game, that's what!" sputtered Mr.
Fulton. "Here, boys, take the canfull in and put it in the shop engine.
If she can take it I guess we're worrying for nothing."

For a moment or so it looked as if that were the case; the engine chugged away in its usual steady manner. But once the gasoline was gone that the boys had been unable to empty out of its tank, it began to kick a little. Within another minute it had stopped dead.

"Show's over," announced Mr. Fulton grimly. "It's way after three o'clock now, and we can't hope to get a new supply from town this side of dark. If we just hadn't sent your auto back!"

"You mean to tell us that you cannot go up—that there will be no flight!" cried Mr. Lewis, making up for all his previous lack of excitement in one burst of protest. "But, man—it's the last day of the option."

"It's worse than that," countered Mr. Fulton. "It's the day before the beginning of a new option, held by the people who watered that gas—and at least a dozen other sneaking tricks."

"But you told us that you would—why, you guaranteed us a trial flight."

"I said you didn't have to buy till you'd seen it work, yes. I'm in your hands, gentlemen. After midnight to-night I'm in other hands—and you're going to lose the chance of your lifetime to secure for your government something that may prove the deciding factor in that terrific war you're carrying on over there. I'm sure you don't doubt my good faith."

"Faith! It's performances we want."

"Give me gas and I'll give you a demonstration that can't help but convince you. I can't use my motor on water. I was willing to risk my neck—and my boy's—by going up and trying this contraption with my left hand—but I can't accomplish the impossible."

"But surely you don't expect us to buy a pig in a poke——"

"This is no pig—it's a hawk. Will you do this? Will you buy the machine and the idea on approval? I'm pledged. If it isn't sold by night to you, to-morrow those other people will come with cash in hand——"

"Harris, you know," drawled Mr. Lewis, "I half believe the fellow's trying to flimflam us, you know. How do we know?"

"How do you know!" Mr. Fulton's eyes flashed fire. "I'll have you know
I'm a man of honor."

"Sure—sure," agreed Mr. Harris conciliatingly. "But that's not the idea, old chap. We don't buy this for ourselves, you understand. We're merely agents, and responsible to our chief. What'd we say if we came back with a bag of pot metal for our money?"

"What will you say to your conscience when your enemy drops destruction onto your brave countrymen in the trenches from the Fulton Aeroplane? That's what you'd better be asking yourselves."

"But we've got to be cautious."

"Cautious! If you saw the goose that laid the golden egg getting off the nest, you'd hold the egg up to a candle to see if it was fresh!"

"Well, now, Mr. Fulton——" began Mr. Harris, when he was interrupted by Jerry, who had been holding himself in as long as was humanly possible.

"Don't let's waste any more time talking, Mr. Fulton. Tod and I have got a scheme that will pull us out on top yet—even if it does mean helping these doubters against their will!"