An abandoned sailboat washes ashore on the island of Amrum. There's no sign of the crew. Then, fishermen pull the body of a woman from the North Sea: Paula Lemmer. She had set sail the previous evening. There's a deep wound on the back of her head, possibly from a blow. Murder cannot be ruled out. John Benthien takes over the investigation and discovers parallels to an unsolved case of a woman murdered in 2005. Back then, as a young detective trainee, Benthien searched for the perpetrator with his mentor, Litmanen. Litmanen disappeared without a trace during the investigation, and his whereabouts remain unknown. John wonders if he made a mistake back then that cost his colleague his life.