Although John Mannering - alias the Baron - had been enjoying his retirement from his 'Baronial' activities as a jewel thief, he was nonetheless tempted by the offer of the strange little Frenchman who visited him late one night. So tempted, in fact, that he accepts, and resurrects the Baron in return for a superb diamond. In doing so, Mannering is plunged into the search for a famous collection of precious stones smuggled into the country by an organization which, he suspects, is also dealing in human contraband.