Lou Bertignac has an IQ of 160 & a good friend in class rebel Lucas. At home her father puts a brave face on things but cries in secret in the bathroom, while her mother rarely speaks & hardly ever leaves the house. To escape this desolate world, Lou goes often to Gare d` Austerlitz to see the big emotions in the smiles & tears of arrival & departure. But there she also sees the homeless, meets a girl called No, only a few years older than herself, & decides to make homelessness the topic of her class presentation. Bit by bit, Lou & No become friends until, the project over, No disappears. Heartbroken, Lou asks her parents the unaskable question & her parents say: Yes, No can come to live with them. So Lou goes down into the underworld of Paris`s street people to bring her friend up to the light of a home & family life.