The narrative traces the trajectory of Gilles (Stéphane Freiss) and Marion's (Valeria Bruni Tedeschi) relationship backward through five stages: 1) Their bleak legal divorce and final hotel room sexual encounter; 2) A tense dinner party with Gilles' gay brother, revealing deep marital fractures; 3) The traumatic premature birth of their son, which Gilles fails to attend; 4) Their wedding night, during which Marion has a spontaneous encounter with a stranger; and 5) Their initial romantic meeting at an Italian beach resort.