make a prisoner of the man whose features would be revealed to him over the wire.
It was a hazardous plan—a risky one—but it the best he could evolve. Tom had instructed Mrs. Damon to keep the man in conversation as long as possible, in order to give the young inventor himself time to rush off in his airship. But of course the man might get suspicious and leave. That was another chance that had to be taken.
"If I had thought of it in time," said Tom, musingly, as he paced up and down in the library waiting for the 'phone to ring, "if I had thought of it in time I would have rigged up two plates—one for a temporary, or looking-glass, picture, and the other for a permanent one. In that way I could rush off as soon as I got a glimpse of the fellow. But it's too late to do that now. I'll have to develop this plate."
Waiting is the most wearisome work there is. Tom and Ned found this to be the case, as they sat there, hoping each moment that the telephone bell would ring, and that the man at the other end of the wire would be the mysterious stranger. Mrs. Damon, too, felt the nervous strain.
"This is about the hour he called up yesterday," said Tom, in a low voice, after coming back from a trip to the window to see that his
