English crime novelist Charles Latimer is traveling in Istanbul when he makes the acquaintance of police inspector Colonel Haki. It is from him that Latimer first hears of the mysterious Dimitrios - an infamous master criminal, long wanted by the law, whose body has just been fished out of the Bosphorus. Fascinated by the story, Latimer decides to retrace Dimitrios's steps across Europe to gather material for a new book. But, as he gradually discovers more about his subject's shadowy history, he gets caught up in Dimitrios's criminal underworld, with unforeseen, life-threatening results.