Alice is a promising young artist in Paris. Her boyfriend Franck, a boxer, has just moved in to her attic flat. Then her sister Elsa, a bored housewife, leaves her unfaithful husband Thomas and turns up unannounced to stay with Alice and Franck. Elsa disrupts their life by playing psychological games with them, but they cannot bring themselves to throw her out.

One afternoon in Saint-Germain-des-Prés, 18-year-old Philippe meets 16-year-old Frédéric. Their eyes meet, they talk and decide to spend a sensemble weekend in Deauville. But it's not that easy to get to know each other. From surprises to concessions, this weekend teaches them how difficult it is to understand each other and not waste the pleasures that come our way; and that sometimes, at the end of the day, we'd like to do the trip all over again, in reverse.

Frédéric is arrested for illicit use of narcotic drugs. In jail, he meets he get up close with various sorts of people among which he looks for a role model as a 18-year-old boy.