Betty is ten years old. She’s scared of ghosts and dark nooks and crannies. When her sister Agnès, who’s a year older than Betty, goes to boarding school, Betty finds herself alone with her parents, Régis and Mado, who are going through a break-up, and Rose, a governess who’s virtually mute.
It’s then that Yvon clambers over the high wall separating the family garden from the psychiatric clinic that her father oversees. Moved by his fragility, Betty hides Yvon for several days in the bike shed. She confides everything weighing on her heart to him, determined that he’ll become her best friend and confidant.
Yvon barely communicates. However, little by little, a bond of trust, then a kind of friendship forms between them. But the hiding place isn’t secure and Yvon refuses to stray from it alone. So Betty decides to run away with him.