Tit. orig.: Sjöjungfrun

After a man disappears in Fjällbacka, Patrik Hedström and his colleagues are unsure if he is dead or alive. When, four months later he is found murdered, frozen in the ice, it comes to light that one of the dead man's acquaintances, author Christian Thydell, has begun receiving anonymous threats. When he receives a threat during the launch party for his breakthrough novel, he breaks down and shows the letters to Erika Falck, who helped him with the manuscript. He refuses to contact the police, and Erika sneaks a letter into her bag and shows it to Patrik. Long suspecting that something is tormenting Christian, she and her husband agree that he is in great danger. When another man is found murdered, the police realize that there is a connection.