In 1991, at a youth camp run by the Norwegian Salvation Army, the 14-year-old daughter of a senior Salvationist official is raped in a public toilet. Because of the Salvation Army's strict hierarchical setup, and also because revelation of the rape will severely damage the organisation's reputation, she does not tell anyone about the ordeal. The name of the assailant is not given. That same year, during the breakup of Yugoslavia, a young Vukovar Croat fighter witnesses atrocities committed by the victorious Serb militias in the aftermath of the Battle of Vukovar. The fighter, who receives the nickname "Little Redeemer", later becomes a professional assassin, who carries out contract killings in various European cities.

In the present day (2003), the assassin – calling himself Stankić – arrives in Oslo and kills a Salvation Army officer during a Christmas street concert. Stankić has a facial anomaly known as hyperelasticity, wherein his facial muscles can be manipulated voluntarily to stop people from recognizing him. As such, despite the murder happening in a public place, the Norwegian police get little useful information regarding the killer. Meanwhile, retiring Oslo police inspector Bjarne Møller gives his three main officers. – Jack Halvorsen, Beate Lønn, and Harry Hole – gifts. Hole's is a wristwatch which grows to annoy him due to its incessant ticking. Møller is replaced as senior police inspector by Gunnar Hagen.

Hole, Halvorsen, and Lønn are assigned to the murder of the Salvation Army officer, Robert Karlsen. When a murder attempt is made on Robert's brother Jon, it is believed that the Karlsen family is being attacked. With Hole's former girlfriend, Rakel Fauke, having left him and started seeing another man, Matthias Lund-Helgesen, Hole meets – and eventually begins a relationship with – Martine, the young woman who (unbeknownst to Harry) was raped in 1991. Hole finds clues that lead him to Croatia and to Stankić's minder, who is revealed to be the assassin's mother. He makes a deal with her to save her son's life, but upon returning to Norway discovers that a man wearing Stankić's clothes has been shot and killed by a police marksman. The dead man's face is all but obliterated and identification is near-impossible.

Halvorsen, Lønn's boyfriend, is fatally wounded outside Jon Karlsen's flat. Afterwards, Hole discovers that the blood of the dead man does not match that of Stankić, whose blood was found at the scene of Halvorsen's attack. Hole continues to follow Stankić, but now knows Jon placed the kill contract on himself by going to Croatia and setting up the hit under the guise of Robert. Jon switched places with his brother so that his murder could not be blamed on him. This had the additional bonus to Jon in that, had Stankić returned home before discovering that he had killed the wrong target, the hitman and his mother would believe they had killed the customer, thus rendering payment impossible and nullifying the need to complete the killing of the 'correct' brother.