* * * * * * * *
In the meantime, Johnny Thompson was in the midst of a strange discovery. Ten minutes after the first message had been delivered, the bell began its jangle once more.
“Hello!” Johnny exclaimed. “Big Ben again!”
Springing to his feet, he began walking back and forth before the round reflector. As on the other occasion, the bell ceased jangling as he passed.
A series of rapid experiments with a hat held in his hand showed him he could shut off the bell by holding the hat in certain positions. These positions, he found, must be higher and higher as he receded from the reflector toward the window.
“One thing I know,” he assured himself. “That sound is produced by some force outside my window. And the person who produces it must be very high up.
“In fact—” He caught his breath as he looked out of the window and away to the east. “There is but one place it could come from. That is the top of the six hundred foot tower of the Sky Ride on those deserted Century of Progress grounds. The Whisperer—”
He broke off short to listen with all his ears. The ringing of that bell ceased, the whispered message was beginning.
* * * * * * * *
What had happened to the slender young detective, Tom Howe? Something rather strange, I assure you.