"They must know how to navigate my aerial warship," thought Tom. "I wonder what their game is, anyhow?"

Night had fallen, but the cabin was aglow with electric lights. The foreigners in charge of the Mars seemed to know their way about perfectly, and how to manage the big craft. By the vibration Tom could tell that the motor was running evenly and well.

"But what happened to the others--to Mound, Ventor and Koku?" wondered Tom.

A moment later several of the foreigners entered. Some of them did not look at all like Frenchmen, and Tom was sure one was a German and another a Russian.

"This will be your prison--for a while," said La Foy significantly, and Tom wondered how long this would be the case. A sharp thought came to him--how long would they be prisoners? Did not some other, and more terrible, fate await them?

As La Foy spoke, he opened a storeroom door that led off from the main, or amidship, cabin. This room was intended to contain the supplies and stores that would be taken on a long voyage. It was one of two, being the larger, and now contained only a few odds and ends of little importance. It made a strong prison, as Tom well knew, having planned it.

One by one, beginning with Tom, the prisoners were taken up and placed in a rec.u.mbent position on the floor of the storeroom. Then were brought in the engineer and a.s.sistant pilot, as well as Koku and a machinist whom Tom had brought along to help him. Now the young inventor and all his friends were together. It took four men to carry Koku in, the giant being covered with a network of ropes.

"On second thought," said La Foy, as he saw Koku being placed with his friends, "I think we will keep the big man with us. We had trouble enough to subdue him. Carry him back to the engine-room."

So Koku, trussed up like some roped steer, was taken out again.

"Now then," said La Foy to his prisoners, as he stood in the door of the room, "I will unbind one of you, and he may loose the bonds of the others."

As he spoke, he took the rope from Tom's hands, and then, quickly slipping out, locked and barred the door.

CHAPTER XXII

APPREHENSIONS

For a moment or two, after the ropes binding his hands were loosed, Tom Swift did nothing. He was not only stunned mentally, but the bonds had been pulled so tightly about his wrists that the circulation was impeded, and his cramped muscles required a little time in which to respond.

But presently he felt the tingle of the coursing blood, and he found he could move his arms. He raised them to his head, and then his first care was to remove the pad of cloth that formed a gag over his mouth.

Now he could talk.

"I--I'll loosen you all in just a second," he said, as he bent over to pick at the knot of the rope around his legs. His own voice sounded strange to him.

"I don't know what it's all about, any more than you do," he went on, speaking to the others. "It's a fierce game we're up against, and we've got to make the best of it. As soon as we can move, and talk, we'll decide what's best to do. Whoever these fellows are, and I believe they are the foreign spies I've been warned about, they are in complete possession of the airship."

Tom found it no easy matter to loosen the bonds on his feet. The ropes were well tied, and Tom's fingers were stiff from the lack of circulation of blood. But finally he managed to free himself. When he stood up in the dim storeroom, that was now a prison for all save Koku, he found that he could not walk. He almost toppled over, so weak were his legs from the tightness of the ropes. He sat down and worked his muscles until they felt normal again.

A few minutes later, weak and rather tottery, he managed to reach Mr.

Damon, whom he first unbound. He realized that Mr. Damon was the oldest of his friends, and, consequently, would suffer most. And it was characteristic of the eccentric gentleman that, as soon as his gag was removed he burst out with:

"Bless my wristlets, Tom! What does it all mean?"

"That's more than I can say, Mr. Damon," replied Tom, with a mournful shake of his head. "I'm very sorry it happened, for it looks as though I hadn't taken proper care. The idea of those men stowing themselves away on board here, and me not knowing it; and then coming out unexpectedly and getting possession of the craft! It doesn't speak very well for my smartness."

"Oh, well, Tom, anyone might have been fooled by those plotting foreigners," said Mr. Damon. "Now, we'll try to turn matters about and get the best of them. Oh, but it feels good to be free once more!"

He stretched his benumbed and stiffened limbs and then helped Tom free the others. They stood up, looking at each other in their dimly lighted prison.

"Well, if this isn't the limit I don't know what is!" cried Ned Newton.

"They got the best of you, Tom," spoke Lieutenant Marbury.

"Are they really foreign spies?" asked Captain Warner.

"Yes," replied his a.s.sistant. "They managed to carry out the plot we tried to frustrate. It was a good trick, too, hiding on board, and coming out with a rush."

"Is that what they did?" asked Mr. Damon.

"It looks so," observed Tom. "The attack must have started in the engine-room," he went on, with a look at Mound and Ventor. "What happened there?" he asked.

"Well, that's about the way it was," answered the engineer. "We were working away, making some adjustments, oiling the parts and seeing that everything was running smoothly, when, all at once, I heard Koku yell.

He had gone in the oil room. At first I thought something had gone wrong with the ship, but, when I looked at the giant, I saw he was being attacked by four strange men. And, before I, or any of the other men, could do anything, they all swarmed down on us.

"There must have been a dozen of them, and they simply overwhelmed us.

One of them hit Koku on the head with an iron bar, and that took all the fight out of the giant, or the story might have been a different one. As it was, we were overpowered, and that's all I know until we were carried in here, and saw you folks all tied up as we were."

"They burst in on us in the same way," Tom explained. "But where did they come from? Where were they hiding?"

"In the oil and gasoline storeroom that opens out of the motor compartment," answered Mound, the engineer. "It isn't half full, you know, and there's room for more than a dozen men in it. They must have gone in some time last night, when the airship was in the hangar, and remained hidden among the boxes and barrels until they got ready to come out and overpower us."

"That's it," decided Tom. "But I don't understand how they got in. The hangar was well guarded all night."

"Some of your men might have been bribed," suggested Ned.

"Yes, that is so," admitted Tom, and, later, he learned that such had been the case. The foreign spies, for such they were, had managed to corrupt one of Tom's trusted employees, who had looked the other way when La Foy and his fellow-conspirators sneaked into the airship shed and secreted themselves.

"Well, discussing how they got on board isn't going to do us any good now," Tom remarked ruefully. "The question is--what are we going to do?"

"Bless my fountain pen!" cried Mr. Damon. "There's only one thing to do!"

"What is that?" asked Ned.

"Why, get out of here, call a policeman, and have these scoundrels arrested. I'll prosecute them! I'll have my lawyer on hand to see that they get the longest terms the statutes call for! Bless my pocketbook, but I will!" and Mr. Damon waxed quite indignant.

"That's easier said than done," observed Torn Swift, quietly. "In the first place, it isn't going to be an easy matter to get out of here."

He looked around the storeroom, which was then their prison. It was illuminated by a single electric light, which showed some boxes and barrels piled in the rear.

"Nothing in them to help us get out," Tom went on, for he knew what the contents were.

"Oh, we'll get out," declared Ned confidently, "but I don't believe we'll find a policeman ready to take our complaint. The upper air isn't very well patrolled as yet."

"That's so," agreed Mr. Damon. "I forgot that we were in an airship.

But what is to be done, Tom? We really are captives aboard our own craft."