“I think I can convince you that I had no part in the smuggling,” spoke Tom, laughing.  “I never sell my airships.  If you like you may talk with my father, the housekeeper, and others who can testify that since my return from taking moving pictures, I have not been out of town, and the smuggling has been going on only a little while.”

“That is true,” assented the custom officer.  “I shall be glad to listen to any evidence you may offer.  This is a very baffling case.  The government is losing thousands of dollars every month, and we can’t seem to stop the smugglers, or get much of a clew to them.  This one is the best we have had so far.”

It did not take Tom many hours to prove to the satisfaction of Mr. Whitford that none of our hero’s airships had taken any part in cheating Uncle Sam out of custom duties.

“Well, I don’t know what to make of it,” said the government agent, with a disappointed air, as he left the office of the Shopton chief of police, who, with others, at Tom’s request, had testified in his favor.  “This looked like a good clew, and now it’s knocked into a cocked hat.  There’s no use bothering that Foger fellow,” he went on, “for he has but one airship, I understand.”

“And that’s not much good.” put in Ned.  “I guess it’s partly wrecked, and Andy has kept it out in the barn since he moved away.”

“Well, I guess I’ll be leaving town then,” went on the agent.  “I can’t get any more clews here, and there may be some new ones found on the Canadian border where my colleagues are trying to catch the rascals.  I’m sorry I bothered you, Tom Swift.  You certainly have a fine lot of airships,” he added, for he had been taken through the shop, and shown the latest, noiseless model.  “A fine lot.  I don’t believe the smugglers, if they use them, have any better.”

“Nor as good!” exclaimed Ned.  “Tom’s can’t be beat.”

“It’s too late for our noiseless trial now,” remarked Tom, after the agent had gone.  “Let’s put her back in the shed, and then I’ll take you down street, and treat you to some ice cream, Ned.  It’s getting quite summery now.”

As the boys were coming out of the drug store, where they had eaten their ice cream in the form of sundaes, Ned uttered a cry of surprise at the sight of a man approaching them.

“It’s Mr. Dillon, the carpenter whom we saw in the Foger house, Tom!” exclaimed his chum.  “This is the first chance I’ve had to talk to him.  I’m going to ask him what sort of repairs he’s making inside the old mansion.”  Ned was soon in conversation with him.

“Yes, I’m working at the Foger house,” admitted the carpenter, who had done some work for Ned’s father.  “Mighty queer repairs, too.  Something I never did before.  If Andy wasn’t there to tell me what he wanted done I wouldn’t know what to do.”

“Is Andy there yet?” asked Tom quickly.

“Yes, he’s staying in the old house.  All alone too, except now and then, he has a chum stay there nights with him.  They get their own meals.  I bring the stuff in, as Andy says he’s getting up a surprise and doesn’t want any of the boys to see him, or ask questions.  But they are sure queer repairs I’m doing,” and the carpenter scratched his head reflectively.