Max, who dreams of adventures, abandons his studies at 18 to become involved in the navy. He becomes the sailor 512.

Claude Massoulier is murdered while hunting at the same place as Julien Vercel, an estate agent who knew him and whose fingerprints are found on Massoulier's car. As the police discover that Marie-Christine Vercel, Julien's wife, was Massoulier's mistress, Julien is the prime suspect. But his secretary, Barbara Becker, while not quite convinced he is innocent, defends him and leads her private investigations.