Betty is ten and is afraid of ghosts and the dark. When her sister leaves home the girl finds herself alone with her parents, Régis and Mado, about to separate, and a housekeeper, Rose, practically mute. It is at this time that Yvon comes over the wall separating Betty's house from the home for the mentally ill that Betty's father directs. Touched by Yvon's fragility, Betty helps her hide for several days. She finally has someone to tell her troubles to and make friends with. But the hiding-place becomes less safe and Betty decides to run away with Yvon.
