As soon as the telephone call had come in, Tom had communicated with a private detective who was in waiting, and this man had gone to the drug store whence the first call had come.  He was going to try to make the arrest of the man telephoning.

But for fear the scoundrel would go to a different instrument, Tom took another precaution.  This was to have one of the operators in the central exchange on the watch.  As soon as Mrs. Damon’s house was in connection with another telephone, the location of the latter would be noted, and another private detective would be sent there.  Thus Tom hoped to catch the man at the ’phone.

Meanwhile Tom listened to the hoarse voice at the other end of the wire, giving the directions to Mrs. Damon.  Tom hoped that soon there would be an arrest made.

Meanwhile the talk was being faithfully recorded on the phonograph cylinder.  And, as the man talked on, Tom became aware of a curious undercurrent of sound.  It was a buzzing noise, that Tom knew did not come from the instrument itself.  It was not the peculiar tapping, singing noise heard in a telephone receiver, caused by induced electrical currents, or by wire trouble.

“This is certainly different,” mused Tom.  He was trying to recall where he had heard the noise before.  Sometimes it was faint, and then it would gradually increase, droning off into faintness once more.  Occasionally it was so loud that Mrs. Damon could not hear the talk about the papers, and the man would have to repeat.

But finally he came to an end.

“This is all now,” he said, sharply.  Tom heard the words above the queer, buzzing, humming sound.  “You are keeping me too long.  I think you are up to some game, but it won’t do you any good, Mrs. Damon.  I’ll ’phone you to-morrow where to send the papers.  And if you don’t send them—­if you try any tricks—­it will be the worse for you and Mr. Damon!”

There was a click, that told of a receiver being placed back on the hook, and the voice ceased.  So, also, did the queer, buzzing sound over which Tom puzzled.

“What can it have been?” he asked.  “Did you hear it, Mrs. Damon?”

“What, Tom?”

“That buzzing sound.”

“Yes, I heard, but I didn’t know what it was.  Oh, Tom, what shall I do?”

“Don’t worry.  We’ll see if anything happened.  They may have caught that fellow.  If not I’ll plan another scheme.”

Tom’s first act was to call up the telephone exchange to learn where the second call had come from.  He got the information at once.  The address was in the suburbs.  The man had not gone to the drug store this time.

“Did the detective get out to that address?” asked Tom eagerly of the manager.

“Yes.  As soon as we were certain that he was the party you wanted, your man got right after him, Mr. Swift.”

“That’s good, I hope he catches him!” cried the young inventor.  “We’ll have to wait and find out.”