Ten years after finishing their studies, Marius Schumann invites his former roommates to the Flensburg Fjord. What was intended to be a fun weekend to rekindle old friendships quickly turns into a nightmare for everyone involved. At first, Marius, Kristina, Jan, and Svenja are happy to reminisce together after such a long time. Together with their partners, they spend joyful hours in Marius' house by the Baltic Sea. However, the idyll soon starts to show cracks. The past has not left any of them unscathed, and there is someone who is playing a sinister game with their fellow human beings. Eventually, one of the guests is found dead in the sauna. As the police begin their investigation, mistrust spreads within the group. It becomes clear that only one of them...