Acclaimed orchestra conductor Thibaut has leukaemia and needs a bone marrow donor. Learning he was adopted, he finds out he has an older brother. Jimmy is a factory worker who plays trombone for a local marching band in Lille. When the band loses its conductor, Thibaut steps in as replacement, and the brothers learn more about the circumstances that shaped each other's lives. Their reunion sparks a fraternal, musical journey amidst the town's factory closure.