Ten-year-old Arthur has just been diagnosed with leukemia. An intense battle begins for the boy and his family. Between trips to the hospital, his mother and father almost forget about his older sister, Viviane, who is also devastated by the ordeal. For her, everything is going downhill: school, friends, her relationship with her parents... Yet she finds the energy to fight for her brother, in her own way. She gets a brilliant idea to bring her favorite animal to him: a therapy horse. The point of view alternates between Arthur and his older sister in this moving story—an experience that will force everyone to grow.