“Of course,” Tom answered.  “Very well, Rad.  You may go on now, and don’t say anything to anyone about what you have told me.”

“I won’t, Massa Tom,” promised the colored man, as he went off muttering to himself.

“Well, what do you make of it, Tom?” asked Ned of his chum, as they walked on toward the shed of the new, big aerial warship.

“I don’t know just what to think, Ned.  Of course things like this have happened before—­persons trying to worm secrets out of Eradicate, or some of the other men.”

“They never succeeded in getting much, I’m glad to say, but it always keeps me worried for fear something will happen,” Tom concluded.

“But about this Frenchman?”

“Well, he must be a new one.  And, now I come to think of it, I did hear some of the men speaking about a foreigner—­a stranger—­ being around town last week.  It was just a casual reference, and I paid little attention to it.  Now it looks as though there might be something in it.”

“Do you think he’ll come to bargain with Eradicate about the mule?” Ned asked.

“Hardly.  That was only talk to make Eradicate unsuspicious.  The stranger, whoever he was, sized Rad up partly right.  I surmised, when Rad said he asked a lot of questions about the mule, that was only to divert suspicion, and that he’d come back to the subject of the fire every chance he got.”

“And you were right.”

“Yes, so it seems.  But I don’t believe the fellow will come around here.  It would be too risky.  All the same, we’ll be prepared for him.  I’ll just rig up one of my photo-telephone machines, so that, if he does come to have a talk with Rad, we can both see and hear him.”

“That’s great, Tom!  But do you think this fellow had anything to do with the fire?”

“I don’t know.  He knew about it, of course.  This isn’t the first fire we’ve had in the works, and, though we always fight them ourselves, still news of it will leak out to the town.  So he could easily have known about it.  And he might be in with those who set it, for I firmly believe the fire was set by someone who has an object in injuring me.”

“It’s too bad!” declared Ned.  “Seems as though they might let you alone, if they haven’t gumption enough to invent things for themselves.”

“Well, don’t worry.  Maybe it will come out all right,” returned Tom.  “Now, let’s go and have a look at my aerial warship.  I haven’t shown it to you yet.  Then we’ll get ready for that mysterious Frenchman, if he comes—­but I don’t believe he will.”

The young inventor unlocked the door of the shed where he kept his latest “pet,” and at the sight which met his eyes Ned Newton uttered an exclamation of surprise.

“Tom, what is it?” he cried in an awed voice.

“My aerial warship!” was the quiet answer.

Ned Newton gave vent to a long whistle, and then began a detailed examination of the wonderful craft he saw before him.  That is, he made as detailed an examination as was possible under the circumstances, for it was a long time before the young bank clerk fully appreciated all Tom Swift had accomplished in building the Mars, which was the warlike name painted in red letters on the big gas container that tugged and swayed overhead.