Roger Marples is halfway across the Atlantic when his ship is blown up beneath him, but not before he found on the person of a fellow passenger (who tried to kill him) half of the plans for a secret weapon. When he is soon rescued by, or accosted by Colonel Granby (depends on your perspective), he is enjoined into taking the deceased passenger's place to head to Germany to get the other half. With Colonel Granby's urging, he will have to take his search into the lair of Hitler himself. Told from Marples' perspective.