The body of a young woman is discovered in a lake, identified as the granddaughter of Hermann Natterer, mayor of the Black Forest town of Klosterbach. Ancient legends talk of ghosts in the lake dragging their victims down to its watery depths. Although all signs point to suicide, Freudenstadt police detectives Maris Bächle and her new partner Konrad Diener have their doubts.
Soon after, another young woman ends up in the deep waters of the lake after plummeting down an incline on her bike. The detectives find a connection between the cases: The two women knew each other, and both had secretly met with a stranger.