Thibaut is a world-renowned symphony orchestra conductor. After a visit to the doctor's office, he learns that he has leukemia and urgently needs a bone marrow donor. His life is turned upside down, especially when another crucial event arises. A DNA test reveals that he is adopted and has a biological brother. This brother is Jimmy, a cafeteria worker in Lille, a working-class city in northern France. They share almost everything—except blood ties and a love of music. It turns out that his newfound brother plays the trombone in the local marching band. Their initial tense meeting develops into a deep brotherly bond, especially when Thibaut takes over as conductor of Jimmy's orchestra, determined to help it win a regional competition.