As the film begins, journalist Abel (Louis Garrel) is having a conversation with his long-time girlfriend Marianne (Laetitia Casta), who has news for him: she’s pregnant, but their mutual friend Paul, and not Abel, is the father. Marianne impetuously announces that she and Paul are getting married, throwing Abel’s life into chaos. Fast-forward a decade later, Abel has rebuilt himself, although he has never found anyone who entranced him the way Marianne did.
Un Hombre Fiel (A Faithful Man) follows at Paul’s funeral, where Marianne and Abel revive their friendship, much to the dissatisfaction of Joseph (Joseph Engel), Marianne’s nine-year-old son. Young Joseph isn’t the only one disappointed in the reconstituted sparks between the couple, as Eve (Lily-Rose Depp), Paul’s younger sister, has had a crush on Abel for most of her life. When questions begin to appear around the nature of Paul’s death, the machinations and jealousies of Joseph and Eve begin to weaken the foundation of Abel and Marianne’s new relationship.