Detective Sergeant Timo Harjunpää of the Helsinki Violent Crimes Unit is an honest and conscientious cop who loses his daughter in tragic circumstances. Despite the support he receives from his colleague, Constable Onerva Nykänen, Harjunpää is unable to recover from his loss. While he looks for a way to assasinate his daughter´s killer, he works on various cases involving strange deaths at Helsinki´s metro stations, eventually determining them to be serial killings. But while he seems to get closer to the killer, the killer is actually getting closer to him. Harjunpää must find the murderer and as he tracks him down, Harjunpää encounters an overwhelming darkness both within himself and without.