Catherine (Ardant) and Bernard (Depardieu) are a middle-aged married couple. One day she finds out that he's been cheating on her, but he dismisses the affairs as meaningless and assures her he still loves her. Unconvinced, Catherine goes into a sex club one night and meets a beautiful prostitute named Marlene (Beart). Catherine hires Marlene, giving her the codename Nathalie, to seduce and spy on Bernard and report their meetings to her.
The film got a 2009 Hollywood remake titled Chloe, which has some drastic differences in terms of the direction the plot takes.
Nathalie... provides examples of the following tropes:
- Did They or Didn't They?: Towards the end, after Marlene admits to Catherine she was lying about sleeping with Bernard the whole time, she caresses Catherine's hair, they embrace deeply and then the scene fades to black, which may or may not mean they had sex.
- Fetish: Although she's not aware of it at the start, it quickly becomes clear that Catherine is less bothered by Bernard's cheating than she is interested in hearing the lurid details of Nathalie's encounters with him.
- Imaginary Love Triangle: Catherine sets up a love triangle by hiring a prostitute to have an affair with her husband. Or so she thinks. Bernard never paid much attention to Marlene and forgot she existed after their first and only meeting, so Marlene made up stories so she could still get money out of Catherine.
- Odd Friendship: Although Catherine hired Marlene's services for her husband, which is something she's pretty ambivalent about, they end up developing a friendship, as Catherine often seeks out Marlene to confide to her about her insecurities in her marriage and sex, and Marlene eventually starts showing genuine concern for her.
- Sexless Marriage: Bernard complains to Catherine that they haven't had sex in forever, which he uses as justification for why he sought out other women.
- Sleep Cute: After a girls' night out, Catherine falls asleep with her head on Marlene's shoulder and her hand on her arm.
- Unproblematic Prostitution: Marlene for a prostitute is a pretty well-adjusted person with a good social life, and never gets into risky situations that threaten her well-being. She treats her job as something that pays the bills while she's training to be a beautician.
- Unresolved Sexual Tension: Catherine and Marlene's encounters are loaded with sexual tension as Marlene relates the details of her affair with Bernard. The scene in the hotel room and the one where Marlene stays the night at Catherine's childhood home and sleeps in her bed (but not with her) stand out. Whether anything actually comes of it is up to one's interpretation of a scene near the end.
- Your Cheating Heart: Bernard being unfaithful to his wife Catherine is what kickstarts the plot, although he insists his encounters are all about sex and mean nothing to him. Midway through the film, Catherine tries sleeping with a different man herself and enjoys it.