Thirteen-year-old Lou Bertignac is a gifted but lonely child. At high school she is already in fifth grade, two years ahead of the other students, but she has no friends. At home, she does not feel too good between a father who is a stickler over principles and a deeply depressed asthenic mother. When the French teacher asks the class to write an essay and to make a presentation about a subject of their choice, Lou chooses homelessness. She hopes to be helped by a homeless girl she has noticed at the Gare d'Austerlitz, who begs and asks for cigarettes there. Nora, nicknamed No, reluctantly accepts to be interviewed by the serious-minded child. They meet several times at the café and although No is intemperate and unpredictable, a little frightening in fact, Lou soon cannot do without her any more...