Marco, a penniless nobleman, unhappily married to the rich Dorothy, and her best friend, Gianna is his mistress who, one day kills his wife. He automatically becomes the administrator of her estate - which, however, at the age of twenty it will have to pass to Nancy, Dorothy's daughter from her first bed. Marco retires to live with Gianna in the luxurious villa on the shores of a lake. Here the pretty future heir reaches him, whom he had never known. Nancy has been in a boarding school for a long time and hasn't seen her mother very often. To avoid having to renounce the enjoyment of the rich life, Gianna encourages him to kill the girl. But the man ends up falling in love with her and the same thing happens to Gianna. And there is a surprise visitor.