A keen student of human nature, Moscrop concentrates his interest on one particular family of holidaymakers-- the Protheros, and especially the beautiful Zena Prothero, whose husband appears to take her excessively for granted. Gradually Moscrop moves into the circle of the Prothero family, only to become involved in a sensational murder. All Brighton is horrified by the gruesome crime. The local police seek the help of Scotland Yard, which is provided in the persons of Sergeant Cribb and Constable Thackeray. These indomitable detectives soon find themselves challenged by the strangest case of their careers, one that is as mystifying as it is macabre.