Justin March is urgently summoned by his old friend, the British Minister of Security, to take some time off from his work with British Intelligence and look into the matter of "a sinister and brutal master-criminal, a one-time Gestapo agent who would stop at nothing" - a man known in the shadows only as 'the Emperor'. This dangerous assignment will lead March eventually to the frightening old dungeons at Pentover Castle where the Emperor waited - and smiled. "It was the smile of a human wolf".