For the moment, the affairs of Dick Donovan,—our readers will have guessed that this first aerial stowaway on record was the young reporter,—had to wait. This drop through space was too thrilling, daring, dangerous for anyone on board to pay Dick more than passing attention. There was not even time to ask him who he was.

Indeed, at the instant that Dick, who had hidden in the machine without any idea that immediate flight was to be undertaken, made himself known, peril loomed swiftly and ominously before them.

As they swooped downward, like a giant fishhawk diving after its finny prey, there was a sudden shout of alarm from Tom. The great airbag swung to one side, dragging the carriage of the flying machine with it in a dizzying swerve.

“Look out!” shouted Tom excitedly.

There was no need to ask him the cause of his sudden alarm. The Wondership, yawing before a sharp flaw of wind which came too suddenly for Jack to counter it, was being driven straight for one of the slender, sharp-topped masts of the yacht.

“Keep her off!” shouted Mr. Chadwick, half rising, “we’ll rip the bag open if you don’t look out.”

Jack’s lips set grimly, determinedly. With a swift motion of his hand he applied power. The propeller began to whirl, forcing the wind-driven craft away from the peril of the mast. Dick Donovan, in frank terror, shouted aloud.

“Gracious! We’ll strike!” was the cry forced from Tom’s lips.

The next instant, despite Jack’s prompt action, the Wondership, deliriously sagging and swaying, crashed against the tip of the yacht’s after mast.

Ri-i-i-i-i-i-i-i-i-p!

The steel tipped weather-vane that was fixed on the top of the spar had penetrated the midship section of the bag and inflicted a bad tear in it before Jack had had time to hold the big craft off. The propeller had been set in motion an instant too late. With a vicious hissing sound the gas rushed from the rent as the Wondership, the mischief done, careened drunkenly away from the mast that had inflicted the wound.

There was a sudden, appalling dash downward. A stone from a roof could not have fallen much faster. Amidst a shout of alarm from the yacht’s decks, which was echoed by those on the Wondership, she struck the sea with a force that sent spray and foam half way as high as the vessel’s mast heads.

In the dreadful moment that succeeded, it seemed as if the craft must go crashing down to the very floor of the ocean. But a fraction of a second later those on board both Wondership and yacht knew that this was not to be the case.

Having struck the water, the hollow hydroplanes and the water-tight body of the craft fulfilled their purposes right nobly. Buoyed on the crest of a big swell, the Wondership floated, and the next instant, amidst a cheer of more than ordinary fervor, Jack started her for the yacht’s side.

“Hurrah! She floats!” yelled Tom.

“By the galumping galleons of Gaul, she does that!” agreed Dick Donovan, against whose pale face the freckles stood out like spots on the sun.

“But will she move?” cried Mr. Chadwick, as the propeller began to churn the water.

“We’ll soon see,” answered Jack over his shoulder.

As the blades bit into the water the Wondership was drawn forward, slowly at first and then, gathering speed as she crossed the space intervening between herself and the yacht’s side, the Wondership was seen to adapt herself to the water as well as she had to the earth or the air. A moment later, skillfully manipulating his rudder, Jack brought the strange craft alongside the yacht’s lowered companionway with as much skill as any veteran mariner making a familiar landing.

To reach the gangway from the spot at which the Wondership had struck the water, they had to pass her stern. On the graceful, narrow counter of the craft was much gilt scroll-work and ornamentation. Amidst all this “flummery,” as sailors call it, they made out a name and hailing port.

“Valkyrie-of-Bremen,” was what they read.

As his eyes encountered the name, Mr. Chadwick gave a gasp.

“Why,—why! This is most extraordinary!” he cried in frank amazement. “This is the very yacht from which my wireless message was relayed from Sciuticut!”

“They must have been trying to make for the mouth of the Nestorville River when whatever is the matter on board, came up,” commented Jack.

But by this time they were at the gangway and conversation ceased for the time being. They could see several heads poked over the side, eying them curiously. As they came alongside, a stockily built man with a bristling straw-colored moustache descended the gangway stairs.

He wore a blue coat with brass buttons and appeared to be in authority.

“What’s the trouble?” demanded Jack eagerly, as the man came nearer.

“Good. You saw our signal for aid, then?” he said with an odd sort of hesitation. “You come near wrecking that contraption, just the same,” he added. “What kind of a craft is it?”

“Never mind that now,” exclaimed Mr. Chadwick impatiently. “The question is, do you need help? Are you aground, or what?”

“No, it ain’t that exactly,” said the man slowly; “it’s trouble of another sort.”

“Is this Professor Von Dinkelspeil’s yacht?” asked Jack quickly.

“Sure. Yes, it’s his yacht, all right,” was the odd reply.

“Is the Professor on board?” asked Mr. Chadwick. “He’s a friend of mine, and if he is in any difficulty we shall be glad to do anything in our power to help him out.”

Again the man hesitated. While they had been flinging questions at him he had been joined by another man, a rough looking specimen, clad in a semi-nautical costume. He now turned to this man and they whispered together for an instant. Then the bristly-moustached man turned to our party.

“The Professor is on board,” he said, “but I don’t know if you can see him.”

“Why not?” demanded Mr. Chadwick crisply, with rising irritation. “You signalled us for aid, we came out here at considerable risk and, in fact, have seriously damaged our craft. If the Professor is on board, I think he owes us an explanation.”

Once more there was a whispered conversation.

“There’s something extremely odd about all this,” said Mr. Chadwick to Jack in an undertone. “I can’t understand it at all. I——”

“The fact is,” broke in the bristly-moustached man, “the Professor has met with an accident. But perhaps you had better come on board and see him for yourselves.”

“I guess that would be the best plan,” said Mr. Chadwick. “Boys, you wait here. I’ll be back before long.”

“I don’t half like the look of this,” muttered Jack. “There’s something here that isn’t all right. Let me go with you.”

“No, my boy. You stay where you are. I’ll be back before long. I can’t imagine what can be the matter; but whatever it is, I can take good care of myself.”

With these words Mr. Chadwick sprang to the platform of the gangway, and under the guidance of the two men he made his way up the steps. An instant later he was gone from view.

The boys exchanged glances.

“Well,” blurted out Tom, “if this doesn’t beat the band! These fellows waste powder enough for a Fourth of July celebration to summon aid, and when it comes they don’t appear to know whether they want it or not.”

“Looks mighty fishy,” admitted Jack. “I wish Dad had let me go with him. But see here, Tom, we’re forgetting all about our stowaway. Say, who are you, anyhow?” he demanded, turning to Dick Donovan and scrutinizing him sharply. Dick looked considerably abashed.

“I guess it’s up to me to make explanations,” he said. “My name is Dick Donovan. I’m a reporter. I was told to run down the ‘Mystery of the Skies’ or get fired. I sneaked into your shed when you went out to take a look at this yacht, and then when you came back unexpectedly while I was snapping your machine, I got rattled and hid under the seat. Wow! By the sky-scraping sultans of Syria, but you gave me a royal old scare!”

“That is nothing to what you are going to get if you write a line about all this in your paper,” snapped Tom. “What do you mean by playing the sneak about our work-shed and spying on us,—eh? What do you mean by it?”

He doubled up his fists threateningly; but Dick Donovan only smiled.

“Don’t get mad,” he said. “I’ll admit it wasn’t the right thing to do, and you chaps appear to be pretty white and I’m ashamed of myself for spotting you.”

“You ought to be,” growled Tom.

“Wait a minute,” put in Jack soothingly. “Go on,” he remarked to Dick Donovan.

“Oh, well, all I wanted to say was this,” said the reporter, getting very red. “You needn’t be afraid that I’ll write a line about this thing, because I won’t. I can get another job somehow, I guess, and anyhow I’ve had enough experience crammed into this last half hour to be able to sit down and write a novel.”

The impulsive Tom’s manner changed in a jiffy.

“Say, you’re all right, Donovan,” he exclaimed, “and—and I tell you what, when we get this thing perfected we’ll give you the first news about it,—a scoop, don’t you call it?”

Dick’s amiable face beamed broadly as Jack nodded his assent to Tom’s promise.

“Say, that’s bully of you!” he cried boyishly, extending his hand. “I don’t want you to think I’m a bounder just because I came peeping and peering about your shack back there. I didn’t look at it from your point of view. I——”

He broke off abruptly. His lower jaw remained dropped just as it had been as he was about to continue speaking. At the same instant both the Boy Inventors sprang to their feet.

It was a startling enough interruption that had occurred to cut short Dick Donovan’s contrite speech.

From the decks of the Valkyrie there had come the sharp, ringing report of a pistol.

It was followed by shouts and a loud tramping of feet on the planks above them. Jack paused a second for thought and then, grabbing up a monkey wrench and calling to the others to do the same, he jumped for the companionway.