For a second the whisper ceased. There was something awe-inspiring about that whisper. As he sat in his secret chamber away up there against the sky, Curlie felt as if some spirit-being was floating about out there in the sky on a fleecy cloud and pausing now and then to whisper to him.

"I saw you," the whisper repeated. "You are in very grave danger. He is a bold and treacherous man. It's big, Curlie, big!" The whisper rose shrilly. "But you must be careful. You must not let him know the place where you listen in. I don't know where it is. But I do know you listen in. Be careful—careful—careful, c-a-r-e-f-u-l-" The whisper trailed off into space, to be lost in thin air.

Wiping the beads of perspiration from his face, Curlie sat up. "Well, now," he whispered38 softly to himself, "what do you know about that?

"One thing I do know," he told himself. "I'd swear it was a girl's whisper, though how you can tell a girl's whisper is more than I know. Question is: Which one is it—hotel station or the one that moves?"

For a moment his brow wrinkled in thought. Then with an exclamation of disgust he exclaimed:

"That's easy! I've got their location!"

He figured for a few seconds, then put a pencil point on a certain spot on his map.

"There!" he muttered. "It's the hotel, the exact spot."

Suddenly he started. There came the rattle of a key in the door.

"Oh!" he exclaimed as Coles Masters shoved the door open, "it's you. I'm glad you're here. Got something I want to look into. Want to bad. Mind if I take an extra hour?"

"Nope."

"All right. See you later." With a bound39 he was out of the door and down the stairs.

"That boy," muttered Coles Masters, with a grin, "will either