Camille, 13, sees her world change when her mother tells her that she has leukemia. Welcomed by her aunt Loulou, her mother's identical twin sister, the teenager then plunges into the strange universe of the seventh and a half floor, where her usual landmarks have disappeared: she now lives with her mother's double, has to face to the teasing and uneasiness created around her at school, and to her own fear of losing the pillar of her life. An unexpected friendship, Loulou's support and a guitar will help her navigate her way through the chaos.