A small town is terrorized by a serial killer. Lauri finds a dead body on his way to the university, reports it to the police and gets tormented by an obsessed police officer. At the same time Lauri's old friend returns to town.

The dirty cop begins with Inspector Relander's cold-blooded murder, which is investigated by the police duo Raittinen (Raunio) and Jokinen (Kulmala). Jack (Tuiskinen), a hard-core member of the Teisko mafia, is also involved in the murder. Behind the assignment is the mysterious Mr. Rönkvist. Is Rönkvist ultimately a man or a myth?