Brighton, 1882: Albert Moscrop spends his holiday peering at beachgoers through a telescope, piecing together disarmingly trivial observations into a compelling drama for his own amusement. A keen student of human nature, Moscrop concentrates his interest on one particular family—the Protheros, especially the beautiful Zena Prothero, whose husband appears to take her for granted. Moscrop gradually moves into the circle of the Prothero family, only to become involved in a sensational murder. All of Brighton is horrified by the gruesome crime, and the local police seek the help of Scotland Yard’s Sergeant Cribb and Constable Thackeray, who soon find themselves challenged by the strangest case of their careers, one as mystifying as it is macabre.