In Paris, the executive Bernard (Gérard Depardieu) and his wife, the gynecologist Catherine (Fanny Ardant), form a bored upper class middle aged bourgeois couple. They have been married for many years and their life does not have sexual desire anymore. One day, Catherine listens to the message box of his cell phone and she believes Bernard is unfaithful to her. Catherine hires the beautiful prostitute Marlene (Emmanuelle Béart) to pretend to be a young woman called Nathalie, seduce and investigate the sex life of Bernard and report to her his secrets and performance between walls. Catherine discloses a surprising revelation in the end.