A body is found in a boat adrift somewhere between Fort Boyard and Aix Island. Solène Brach from the mainland police is sent to investigate. She asks for assistance from Vincent, mayor of the island, but he is reluctant to be part of the investigation. The victim, José Chebec, a native of the island, had just got out of prison after 20 years, and was working as the guard of the fort. He'd been involved in a jewelry heist that had gone wrong, resulting in two deaths. José got 20 years while his accomplice, Michel, was never found. Michel's wife, Aline, raising their son Mathieu by herself, has never given up on her husband still being alive. Through the criminal investigation, the whole life of the island, with its silences, mysteries and family secrets, is turned upside-down.