In this drama about life and death in the fast, middle, and slow lanes, Juliette (Carole Laure) finds herself stranded on a busy highway leading from Paris south to cities like Lyon. She was supposed to meet her lover, and is driving his car when she stops at their appointed roadside rendezvous. Instead, their deception has been discovered by her lover's wife, who is waiting for her, and drives the car away in a huff. Juliette is left to thumb it back to Paris. She soon hooks up with Arthur Colonna (Jean Yanne), who gives her a ride, and the two begin to wend their way northward along the highway. Interspersed with their journey is a series of cinematic "asides" that delve into tragic mishaps, such as the aftermath of a crash in which a woman was killed, her husband stumbling along the highway, still in shock -- and the brief story of a surgeon named Kalendarian (Georges Wilson) who struggles to find the needed transfusions for the crash victims on this busy weekend. The relationship between Juliette and Arthur begins to turn from casual to interested when they suffer a bad accident from which they both manage to come out unscathed -- leaving an indelible effect on their growing relationship.