The film follows Maxime Nathan and his Jewish family in France during the years leading up to World War II. François Grimbert (played as a young boy by Valentin Vigourt and as an adult by Mathieu Amalric) grows up in Paris in the 1950s. He is the skinny, sickly son of two marvelously athletic parents, Tania (Cécile de France) and Maxime (Patrick Bruel). For a while, he dreams of a stronger, fitter, more charismatic older brother to compensate for his own feelings of inadequacy. Only gradually does he learn of his parents' tragic past and that he has a sibling — a half-brother named Simon, his father's first son.