“Pete’s sake! What wave-length do you use?” “I don’t know.” “What?” “Only one person in the world knows that. He’s the man who made it. My old friend C. K. All I know is, it’s very short. Watch!” She snapped off the lights, then pulled down the shades. The radio’s tubes glowed red. “Say! A radio with its own private wave length is worth a fortune! I know a man high up in Communications. Let me show it to him.” “Not for worlds.” “You’ll be rich and famous.” “No! No! Oh, I wish I hadn’t brought it here. Can’t you see that it was loaned to me by a very dear friend and that he alone can release it?” “Yes,” he replied soberly. “I won’t breathe a word about it until you give me the sign.” “Thanks—oh, thanks!” she stammered. “You really had me worried.” “And now,” he said, “how about having another try at the ‘put-put’ of the gremlins, or subs?” For ten minutes more they sat there in the dark watching the red glow of the strange radio tubes but hearing just nothing at all. Then, suddenly, it came, a low “put-put-put-put-a-put-put-put-put-a-put.” For a long time Danny sat there silently listening. “It’s code, all right,” he murmured once. “There’s a sort of rhythm to it, just as there is to all code.” “If you turn this dial,” Sally whispered, “it will throw them out.” She turned the dial. Silence followed, but not for long. Again came “put-put-put-a-put.” “They’re back,” he whispered. “No, that’s another one. Listen! You can tell the difference.” She brought the first one back, then switched to the second. “What do you know about that!” He was all ears.