A stormy wind lashes the deserted beach of Spiekeroog. Only a solitary vacationer braves the weather and discovers a man in beach chair 513, whose body is oddly contorted. He can't be sleeping; he's dead! Karl-Dieter fetches his friend, Detective Mütze. Together they stand in front of the beach chair - it is empty and carefully screened. No body, no murder. That's it. The two friends enjoy their island holiday until a dead woman is found on the beach. The island policeman Ahsen, who specializes in recovering stolen beach carts, is satisfied with the explanation of suicide. However, there is a connection between the dead woman and the mysterious beach chair 513. Now, Mütze, with the support of Ahsen and Karl-Dieter, begins the investigation. Little do they know the depths they are about to explore...