“Customs department!” gasped Tom.  “You want to ask me some questions?”

“That’s it,” went on the man, in a business-like voice.

“What about?”

“Smuggling by airship from Canada!”

“What!” cried Tom.  “Do you mean to say you suspect me of being implicated in—­”

“Now go easy,” advised the man calmly.  “I didn’t say anything, except that I wanted to question you.  If you’d like me to do it out here, why I can.  But as someone might hear us—­”

“Come inside,” said Tom quietly, though his heart was beating in a tumult.  “You may go, Koku, but stay within call,” he added significantly.  “Come on, Ned,” and he motioned to his chum who was approaching.  “This man is a custom officer and not a spy or a detective, as we thought.”

“Oh, yes, I am a sort of a detective,” corrected Mr. Whitford.  “And I’m a spy, too, in a way, for I’ve been spying on you, and some other parties in town.  But you may be able to explain everything,” he added, as he took a seat in the library between Ned and Tom.  “I only know I was sent here to do certain work, and I’m going to do it.  I wanted to make some observations before you saw me, but I wasn’t quite quick enough.”

“Would you mind telling me what you want to know?” asked Tom, a bit impatiently.  “You mentioned smuggling, and—­”

“Smuggling!” interrupted Ned.

“Yes, over from Canada.  Maybe you have seen something in the papers about our department thinking airships were used at night to slip the goods over the border.”

“We saw it!” cried Tom eagerly.  “But how does that concern me?”

“I’ll come to that, presently,” replied Mr. Whitford.  “In the first place, we have been roundly laughed at in some papers for proposing such a theory.  And yet it isn’t so wild as it sounds.  In fact, after seeing your airship, Tom Swift, I’m convinced—­”

“That I’ve been smuggling?” asked Tom with a laugh.

“Not at all.  As you have read, we confiscated some smuggled goods the other day, and among them was a scrap of paper with the words Shopton, New York, on it.”

“Was it a letter from someone here, or to someone here?” asked Ned.  “The papers intimated so.”

“No. they only guessed at that part of it.  It was just a scrap of paper, evidently torn from a letter, and it only had those three words on it.  Naturally we agents thought we could get a clew here.  We imagined, or at least I did, for I was sent to work up this end, that perhaps the airships for the smugglers were made here.  I made inquiries, and found that you, Tom Swift, and one other, Andy Foger, had made, or owned, airships in Shopton.”

“I came here, but I soon exhausted the possibility of Andy Foger making practical airships.  Besides he isn’t at home here any more, and he has no facilities for constructing the craft as you have.  So I came to look at your place, and I must say that it looks a bit suspicious, Mr. Swift.  Though, of course, as I said,” he added with a smile, “you may be able to explain everything.”