“I don’t rightly know. I went up to that floor a few minutes ago, but no one was in sight then. Maybe they were there half an hour; maybe only five minutes.” “What did they look like?” The janitor scratched his head. “Well, now, I didn’t pay a whole lot of attention to them. One of them was a lot taller than the other one, though.” A premonition had been growing on Bob and he couldn’t repress his question. “Did the taller one have red hair?” he asked. “Come to think of it, he did,” replied the janitor. “And the shorter one; was there a scar on his forehead?” “That’s right. Friends of yours, of course?” “Well, not exactly friends,” said Bob. “Remember anything else about them?” asked Merritt Hughes. “Not right now, anyhow,” said the janitor and they left him to return to his work while they went outdoors. Merritt Hughes was the first to speak. “I guess there is no question about the identity of your visitors. They are the same ones who attempted to kidnap you. What’s the reason for all of your popularity?” Bob shook his head. “I only wish I knew,” he said. “Believe me, it is no fun to have your room torn apart like that. Why they ruined my clothes and it’s going to be mighty costly getting them repaired.” “I’ll help you out if you’re pinched for money,” volunteered his uncle, reaching for his billfold. But Bob waved the offer aside. “Thanks, but I’ll get along all right. If I ever catch up with those fellows they’ll have to get their fists into action pretty fast if they want to escape a thorough drubbing.” “I don’t blame you a bit for feeling that way. But we’ve got to get along. I have an appointment with one of the army’s chief radio engineers in less than fifteen minutes and I want you to sit in.” They signalled for a cab and started for the meeting which was to reveal some startling information on Bob’s first case. Chapter XVII THE RADIO SECRET ★ Merritt Hughes leaned back in the seat as the cab darted in and out of the heavy traffic on the avenue. “All of the breaks have been against us so far,” he mused, half to himself and half to Bob, “but we’re bound to find something coming our way soon.” “I’m anxious to see the fellow who is being held at the police station,” said Bob. “Surely you’ll be able to get some information out of him.” “Remember you’re working on this case, too. Better say ’we’ instead of ’you’ when you’re talking about it. This is the firm of Hughes and Houston, working for Uncle Sam on a radio mystery.” Their cab pulled up in front of the War Department and they entered and hastened to an upper floor where the federal agent rapped sharply on a door marked “Major Francis McCreary, Private.” “Come in,” a heavy voice on the other side rumbled and Merritt Hughes opened the door.