Mamadou Ba is a public letter-writer. Twice a week, he offers his services in a house in Montreuil, a suburb of Paris. There we meet a father who wants better housing, a dismissed worker, an undocumented man, a request for naturalisation, etc. The list is long. Over the course of these exchanges, a portrait of Mamadou gradually emerges through his work, which he sees as a mission: to help his immigrant brothers and sisters with their administrative tasks.