Marc, who shares a remote mountain chalet with his sister, teaches literature at the polytechnic beside the lake in Lausanne and cannot resist his female students. One of them, Barbara, in the morning is dead in his bed. When she is reported missing, the police open an enquiry and her glamorous young stepmother Anna starts her own investigation. Anna easily seduces the ever-amorous Marc, while he at the same time is unsuccessfully fending off both a sexy young student Annie and his frustrated spinster sister Marianne, who is being wooed by Richard, his head of department. But the police are closing in and Anna may not be what she appears.