The whole thing started when the clock on the Metropolitan Tower began to run backward. It was not a graceful proceeding. The hands had been moving onward in their customary deliberate fashion, slowly and thoughtfully, but suddenly the people in the offices near the clock's face heard an ominous creaking and groaning. There was a slight, hardly discernible shiver through the tower, and then something gave with a crash. The big hands on the clock began to move backward...