"Yes, and they must be here now.The placing of that copper bar proves it.""Then let's make a search and find them, Tom.It must be some of those foreign spies.""Just what I think."
But a more careful search of the craft than the one Tom had casually made revealed the presence of no one.All the crew and helpers were accounted for, and, as they had been in Tom's service for some time, they were beyond suspicion.Yet the fact remained that a seemingly human agency had acted to put the main motor out of commission.Tom could not understand it.
"Well, it sure is queer," observed Ned, as the search came to nothing."It's worse than queer," declared Tom, "it's alarming! I don't knowwhen I'll be safe if we have ghosts aboard." "Ghosts?" repeated Ned.
"Well, when we can't find out who put that bar in place I might as well admit it was a ghost," spoke Tom."Certainly, if it was done by a man, he didn't jump overboard after doing it, and he isn't here now.It sure is queer!"Ned agreed with the last statement, at any rate.
In due time the Mars, having fought her way above the storm, came over Shopton, and then, the wind having somewhat died out, she fought her way down, and, after no little trouble, was housed in the hangar.
Tom cautioned his friends and workmen to say nothing to his father about the mysterious happening on board.
"I'll just tell him we had a slight accident, and let it go at that," Tomdecided."No use in causing him worry."
"But what are you going to do about it?" asked Ned.
"I'm going to keep careful watch over the aerial warship, at any rate," declared Tom."If there's a hidden enemy aboard, I'll starve him out."Accordingly, a guard, under the direction of Koku, was posted about the big shed, but nothing came of it.No stranger was observed to sneak out of the ship, after it had been deserted by the crew.The mystery seemed deeper than ever.
It took nearly a week to repair the big motor, and, during this time, Tom put some improvements on the airship, and added the finishing touches.
He was getting it ready for the final government test, for the authorities in Washington had sent word that they would have Captain Warner, in addition to Lieutenant Marbury, make the final inspection and write a report.
Meanwhile several little things occurred to annoy Tom.He was besieged with applications from new men who wanted to work, and many of these men seemed to be foreigners.Tom was sure they were either spies of some European nations, or the agents of spies, and they got no further than the outer gate.
But some strangers did manage to sneak into the works, though they were quickly detected and sent about their business.Also, once or twice, small fires were discovered in outbuildings, but they were soon extinguished with little damage.Extra vigilance was the watchword.
"And yet, with all my precautions, they may get me, or damage something," declared Tom."It is very annoying!""It is," agreed Ned, "and we must be doubly on the lookout."So impressed was Ned with the necessity for caution that he arranged to take his vacation at this time, so as to be on hand to help his chum, if necessary.
The Mars was nearing completion.The repaired motor was better than ever, and everything was in shape for the final test.Mr.Damon was persuaded to go along, and Koku was to be taken, as well as the two government officials.
The night before the trip the guards about the airship shed were doubled, and Tom made two visits to the place before midnight.But there was no alarm.
Consequently, when the Mars started off on her final test, it was thought that all danger from the spies was over.
"She certainly is a beauty," said Captain Warner, as the big craft shot upward."I shall be interested in seeing how she stands gun fire, though.""Oh, she'll stand it," declared Lieutenant Marbury.The trip was to consume several days of continuous flying, to test the engines.A large supply of food and ammunition was aboard.
It was after supper of the first day out, and our friends were seated in the main cabin laying out a program for the next day, when sudden yells came from a part of the motor cabin devoted to storage.Koku, who had been sent to get out a barrel of oil, was heard to shout.
"What's up?" asked Tom, starting to his feet.He was answered almost at once by more yells.
"Oh, Master! Come quickly!" cried the giant."There are many men here.There are stowaways aboard!"
