heard those sounds? Were you near telephone receivers,

touching any part of your sets or doing anything unusual?”

The boys thought deeply, trying to revisualize the conditions that had existed on the few occasions when they had heard the odd buzzing sounds.

“I’m not sure,” said Tom at last, “but it seems to me that when I heard them the first time—that time I was on 23d St., I was sitting close to the telephone receiver on the table—I’d just been called up by Jim and—yes, I am sure now, I remember distinctly—I had my hand touching the stand while I was listening to the messages. You see, I was half inclined to phone to the others to find out if they heard the sounds and I reached out to pick up the phone and then changed my mind—but sort of kept my hand there.”

“Then that’s solved, I think,” declared Mr. Henderson. “If you had taken down the phone receiver and had kept your hand upon it you would probably have heard the other speaker’s voice plainly.”

“Gosh, why didn’t we think of that!” interrupted Frank. “And come to think of it, the phone is on the same table with the radio set at Henry’s house.”

“Well, we’ve laid one ghost, we’ll assume,” went on Mr. Henderson, “but that does not solve the mystery of the other speaker nor does it eliminate the possibility that these fellows may be crooks. In our work, you know, we always assume that every suspect is guilty until we prove our theory wrong and so we’ll assume that your mysterious speaker is a crook until we find we’re mistaken. However, before I take any active steps I think it will be a good plan to try another test. Suppose you listen in for a few nights more and, as soon as you hear this fellow, take down your phone receivers and hold the instrument against your body or arm and see if you get the voice of the other chap. Let me know the results and then we can plan our next move.”

“Hurrah! Now we are real radio detectives working for the government!” cried Tom enthusiastically. “Do you really think they’re bootleggers?”