Carlo (Michele Placido) and Silvia (Fanny Ardant) are a mature, intellectual bourgeois couple who have been married for twenty years. They operate under an explicit, negotiated open marriage agreement ("non-exclusive" arrangement), living in separate quarters while maintaining a deep emotional bond. Carlo lives at their country residence, openly carrying on a romantic and physical relationship with a significantly younger woman, Lù (Giovanna Giuliani). The balance of their arrangement collapses when Silvia begins an intense, raw sexual dynamic with a violent, uneducated young neo-fascist thug (Riccardo Scamarcio). As Silvia openly recounts her explicit physical encounters and her obsession with the youth to Carlo, Carlo is consumed by an all-absorbing retroactive jealousy and psychological fixation. Unable to handle the reality of her new relationship, Carlo’s obsession triggers a destructive downward spiral in their relationship.