Tom could hardly restrain his impatience until Mr. Boylan had
gone. The young inventor had half a notion to produce the other
button, matching the one he had just pulled off his visitor's
coat, and tell where he had found it. But he held himself back. He
wanted to talk first to Ned.

And, when his chum came in, Tom cried:

"Ned, what do you think? I know who had my airship!"

"How?" asked Ned, in wonder.

"By that button clue! Yes, it's the same kind--they're as alike as
twins!" and Tom brought out the button which he had put away in
his desk. "See, Boylan had one just like this on the back of his
coat. The other was missing. Here it is--it was in the seat of my
airship, where it was probably pulled off as he moved about. Ned,
I think I've got the right clue at last."

Ned said nothing for several seconds. Then he remarked slowly:

"Well, Tom, it proves one thing; but not the other."

"What do you mean?"

"I mean that it may be perfectly true that the button came off Mr.
Boylan's coat, but that doesn't prove that he wore it. You can be
reasonably sure that the coat was having a ride in your Eagle, but
was Boylan in the coat? That's the question."