Roubaix, a Christmas night. Commissioner Daoud (Roschdy Zem) travels the city that saw him grow up. Cars burned, altercations...At the police station, just arrived Louis Coterelle (Antoine Reinartz), freshly graduated. Daoud and Louis will face the murder of an old lady. Two young women are interviewed, Claude (Léa Seydoux) and Marie (Sara Forestier). Poor, alcoholic, in love. The film is a polar drawn from a real fact of 2002.