“Hullo! What’s that?”

Tom set down his paint pot and listened intently. Jack crawled out from under the bottom of the Wondership which he had been coating with an extra application of waterproof bronze.

“Sounded like a gun,” he said after a second.

“It did, for a fact. Jove! Hark at the wind.”

As he spoke a gust shook the rather lightly-built shed.

“Must have come on a bit rough while we were at work,” commented Jack. “I hope it isn’t too squally for our trial trip.”

Whatever Tom might have responded to this speech will never be known, for at that instant came another report.

“B-o-o-m!” The echoes came dully shoreward, borne on a flaw of squally wind.

“It is a gun,” cried Tom, “but what in the world——”

“Let’s duck out and see. Hurry up!”

Jack made off and Tom followed. They did not go out of the front end of the shed, though big doors running on rollers opened to seaward. Instead they made for a small “accommodation” door in the rear of the shed. It was alongside this that the watcher had bored his observation hole. He had just time to slip around a corner and fling himself face downward in a patch of spiky sea-grass before the boys ran out.

“Lucky those kids didn’t see me,” he muttered. “I feel half ashamed of spying on them like this. But it’s all in the game, I suppose. If I don’t run down this assignment it means hunting another job, and I’ve worked on every paper in Boston but the one I’m on now; and I haven’t got the fare to go anywhere else job hunting.”

He watched the two boys run up to the summit of a big dune which commanded a broad view to seaward.

“By the horntoads of Herrington,” he exclaimed under his breath, “now’s my chance! I’ll get a few snaps while they’re out of the shed and then dig back. It’s taking a long chance and may be a rotten sort of thing to do, but I’ve simply got to make good.”

He rose from his place of hiding and, dexterously dodging among dunes and sand hummocks, made his way to the shed and darted inside by the small door from which the boys had just emerged. If he was surprised, he counted on managing to hide in some place of security till he got a chance to escape. Dick Donovan, cub reporter on the Boston Evening Eagle, was a young man of much resource, though at present hardly an example to be emulated. Still, as he owned to himself and as his editor had informed him that morning, it was a case of “making good” or getting what the editor termed the “G. B.”—which being interpreted, meant, as poor Dick knew only too well, the “Grand Bounce.”

As is the habit in newspaper offices, such a seemingly hopeless assignment as running down “The Mystery of the Skies” had been given to the cub reporter, the reason being that he might just as well waste his time on that apparently forlorn hope as on anything more promising. But Dick, who was by no means the “bone-head” his indignant editor mentally termed him, worked on the assignment like a beaver. He recalled hearing of the Boy Inventors and their various contrivances, and he formed a conviction that if he could run them down he would arrive at a point near to the solution of the mystery of the flying lights. It had been a matter of some difficulty to find out the present whereabouts of the boys, but the indomitable Dick had finally done it. His inquiries had led him to the lonely shed amidst the wind-driven dunes, and to the beginning of what he would have called “a galloping grasshopper of a yarn.”

As the boys gained the top of the dune they saw the yacht, standing out in white relief against the slaty background of cloud that rolled up from the east. She rose and fell slowly on the sullen sea, and they could see that a vagrant cloud of bluish smoke was rolling away from her. No doubt, then, that it was she that had fired the guns.

By some instinct Jack had snatched up a pair of glasses as they ran out of the shed. They were instruments used by the boys to scan anyone approaching their shed from a distance. He now turned these on the distant yacht. The next instant he uttered an exclamation:

“There’s trouble aboard out there as sure as you’re a foot high!”

“Can you make out what it is? They’re pretty close in, and those Baking Pan Shoals run out quite a way. Maybe they’re aground,” ventured Tom.

“No; it’s not that; at least, I don’t think so. There appears to be trouble on the yacht itself. She’s flying an ensign, Jack down, in her after rigging. Wow!”

“What’s up now?”

“There’s a chap trying to pull the ensign down!” cried Jack, with the glasses still to his eyes.

“Jove!” he rushed on, “there’s another chap pulling him away from the halliards. Now there’s a regular fight on! Say, Tom, that yacht’s just sizzling right now!”

“They need help.”

“Well, it sure looks so! Hullo, some men on the stern appear to have driven back the others, among them the chap who tried to pull down the flag.”

“It’s a sure thing, then, that there is some sort of mutiny on board.”

“Looks that way,” admitted Jack; “they fired those guns for help. I wonder——”

“I have it,” broke in Tom. “There used to be a life-saving station right here because of the shoals. It’s marked on the charts. Although it was abandoned two years ago, those fellows saw our shed ashore and they think it’s the life-saving station. It’s to us they’re signalling!”

“Christmas! I’ll bet you’re right. There’s nothing else in the shape of a house up and down the beach for miles, and the summer cottagers have not arrived yet. Yes, they’re appealing to us, Tom; but I don’t see what we’re going to do about it.”

“You don’t?”

There was an odd look in Tom’s eyes as he spoke.

The next instant there was a flash and a puff of smoke from the stern of the yacht, where Jack had made out some figures standing in a little group. The others had retreated forward. The report of the signal gun was borne to their ears a few seconds later.

“If only we had a boat,” burst out Jack. “I just hate to think of those fellows out there in trouble, and we not able to raise a finger to help!”

“Oh, but we are,” spoke Tom quietly. Jack looked at him swiftly and then almost involuntarily both boys’ eyes rested on the shed behind them.

“Jove, Tom! Have you got the nerve to try it?”

“Sure thing. We planned to make the test anyhow to-day. What better opportunity?”

“It’s blowing up for bad weather, Tom,” remonstrated Jack, who was far less impetuous than his cousin.

“Well, we’ve got to expect to get caught in that sometime. Besides, I don’t think it will blow very hard.”

Like many other people, men as well as boys, Tom had a way of minimizing obstacles when he wanted to do anything very much, and the scene on the yacht had aroused his curiosity to the utmost. Jack thought a minute and then scanned the sky carefully. Dark clouds were piling up and the sea looked leaden and ugly. The wind was not steady but came in sharp gusts and flaws.

“Maybe we’ve got time to get out there and back before it comes on real bad,” he admitted.

“Of course we have. Come on.”

Tom started on a run for the shed that housed the Wondership. As he went, he flung back word to Jack to “hustle.” From the ship came a fourth booming report.

“They’re watching us through glasses,” said Jack, as they ploughed through the sand. “They’ve guessed that we are going to help them somehow.”

“That means that we’ve got to make good,” was Tom’s comment.

They had almost gained the shed door when they saw coming toward them across the dunes a solitary figure, making its way with difficulty over the heavy sand.

“It’s dad!” cried Jack. “He has come to make us a visit, and left the machine back there on the road.”

“That’s so. It is Uncle Chester, sure enough,” assented Tom rather gloomily. “I guess our trial trip is off right now.”

“Yes; I don’t think he’d allow us to take out the Wondership in such weather as this promises to be,” agreed Jack with equal ruefulness. “Still, something should be done to aid those poor people out there.”

“Hullo! What’s the matter with him?” cried Tom in an astonished voice the next instant, for, on seeing the boys, the usually dignified Professor Chadwick had broken into a run. As he floundered along he was shouting excitedly words that they could not catch, and waving something in his hand.