“Put down what you don’t know?” exclaimed Ned.  “How are you going to put down a thing when you don’t know it?”

“I mean we can put a question mark after it, so to speak.  For instance we don’t know where Mr. Damon is, but we want to find out.”

“Oh, I see.  Well, let’s start off with the things we do know.”

The two friends were at Tom’s house by now, having come from Waterford in Tom’s airship.  After thinking over all the exciting happenings of the past few days, Tom remarked:  “Now, Ned, for the things we do know.  In the first place Mr. Damon is missing, and his fortune is about gone.  There is considerable left to Mrs. Damon, however, but those scoundrels may get that away from her, if we don’t watch out.  Secondly, my airship was taken and brought back, with a button more than it had when it went away.  Said button exactly matched one off Mr. Boylan’s coat.”

“Thirdly, Mr. Damon was either taken away or went away, in an airship—­either in mine or someone else’s.  Fourthly, Mrs. Damon has received telephonic communications from the man, or men, who have her husband.  Fifthly, Mr. Peters, either legally or illegally, is responsible for the loss of Mr. Damon’s fortune.  Now:  there you are—­for the things we do know.”

“Now for the things we don’t know.  We don’t know who has taken Mr. Damon away, nor where he is, to begin with the most important.”

“Hold on, Tom, I think you’re wrong,” broke in Ned.

“In what way?”

“About not knowing who is responsible for the taking away of Mr. Damon.  I think it’s as plain as the nose on your face that Peters is responsible.”

“I can’t see it that way,” said Tom, quickly.  “I will admit that it looks as though Boylan had been in my airship, but as for Peters taking Mr. Damon away—­why, Peters is around town all the while, and if he had a hand in the disappearance of Mr. Damon, do you think he’d stay here, when he knows we are working on the case?  And would he send Boylan to see me if Boylan had been one of those who had a hand in it?  They wouldn’t dare, especially as they know I’m working on the case.”

“Peters is a bad lot.  I’ll grant you, though, he was fair enough to pay for my motor boat.  I don’t believe he had anything to do with taking Mr. Damon away.”

“Do you think he was the person who was talking to Mrs. Damon about the papers?”

“No, Ned.  I don’t.  I listened to that fellow’s voice carefully.  It wasn’t like Peters’s.  I’m going to put it in the phonograph, too, and let you listen to it.  Then see what you say.”

Tom did this, a little later.  The record of the voice, as it came over the wire, was listened to from the wax cylinder, and Ned had to admit that it was not much like that of the promoter.

“Well, what’s next to be done?” asked the young banker.

“I’m going to set a trap,” replied Tom, with a grin.

“Set a trap?”