Police Inspector Bruno Baldassarre hears someone screaming from an old palace and finds two dead bodies on the stairs: the owner, Prince Prospero Dell'Orso, and electrician Romolo Colasanti; both were electrocuted. What is apparently an accident soon turns out to be murder. Bruno interrogates the suspects: Anna Dell'Orso, actress and recipient of a large life insurance, and screenplay writer Henry Hermann. Meanwhile, Baldassarre gets to know lovely young Teresa, Colasanti's niece. After more deaths and attempted murders, Bruno realizes that Teresa is Dell'Orso's natural daughter and only heir of his immense riches: she is the murderer's next intended victim...