Rakel is furious with Harry for taking Oleg from the pool and to a location connected to the serial killer. She refuses his offer to drive them home. Harry heads to police headquarters. He speaks with Waaler, who gives him two updates: Only partial fingerprints were found on the television screen, and an autopsy has determined that Camilla was pregnant when she died. She was not known to be in a relationship.

Waaler speaks about his family’s history and pressures Harry to decide about participating in the illicit criminal activities that Waaler facilitates. When Harry hesitates, Waaler gives him two more days to decide.

Late that night, Waaler calls Beate, asking her for any additional forensics information on the case. Beate explains that testing of Lisbeth’s severed finger revealed fecal matter under the fingernail; blood in the fecal matter matches Wilhem Barli’s blood type. Meanwhile, Harry, unable to sleep due to nightmares, calls his friend Øystein (who works as a taxi driver). Oystein comes to Harry’s apartment and gives him drugs to induce sleep. They talk about breaking codes, with Harry expressing his theory that the serial killer is sending them coded messages. Harry also alludes to having been offered a job and being unsure whether to take it.

Harry tracks down Wilhelm Barli at the Theatre Café. When Harry raises the forensic evidence (excrement and blood matching Wilhelm’s type found under Lisbeth’s fingernail), Wilhelm calmly explains that Lisbeth regularly penetrated him during their sexual encounters. He breaks down crying, saying he misses Lisbeth. Harry mentions his troubles with Rakel, and Wilhelm offers him tickets to the opening night of My Fair Lady.

Harry shows Wilhelm a photograph of the devil’s star (pentagram) symbol. Wilhelm says he has seen the symbol before, long ago, but cannot remember where, and promises to call if the memory returns.

Harry has been abstaining from alcohol and suffering from withdrawal. He takes the sleeping pills that Oystein gave him and falls into a trance state. Over the course of the night, Rakel calls to apologize. When he wakes at dawn, he realizes he has cracked the code: the number 5 is at the center of everything.

Meanwhile, in the storyline set in Prague, Eva frets about her lover’s frequent trips to Oslo. She fears that he may be having an affair and she is especially anxious because she is pregnant. Looking for information, she opens his suitcase while he is sleeping and finds a gun. She resolves not to pry into his life, even if he may be engaging in criminal activity. In the morning, she tells him that she is pregnant. He reassures her that visits to his mother are the reason for his frequent visits to Oslo and gives her a necklace with a star-shaped diamond. When Eva mentions the gun, he shows it to her along with the silencer, saying she needs to know who he truly is.

Harry hurries to the office and calls a 1:00 pm meeting with Møller, Waaler, Beate, and Aune. He reveals his discovery: the killer’s code is the number five. The diamond has five sides, five days separate each murder, the crimes occur around 5:00 pm, and all victims died on the fifth floor. Harry also shows them a map of Oslo with a devil’s star projected onto it, showing that the three crime scenes form three points of a pentagram.

The remaining two points reveal the next murder locations: a student building near Ensjøveien in Kampen and Villa Valle, a historic house inhabited by an elderly woman named Olaug Sivertsen. With five days between murders, the next killing is predicted to happen on the following day.

With further crimes impending, Waaler proposes a carefully planned operation focusing on the student building and says he will contact Special Forces. Harry and Beate volunteer to visit Olaug Sivertsen.

Otto Tangen, owner of the surveillance company Harry Sounds, receives a late-night call from Tom Waaler requesting urgent installation of surveillance equipment in a student building. When Otto insists the job cannot be completed overnight, Waaler reveals he knows the location of Otto’s undeclared surveillance equipment hidden in a barn in Asker. Blackmailed, Otto reluctantly agrees, understanding he has no choice.

Harry and Beate visit Olaug Sivertsen at Villa Valle. They warn her about the danger, but she takes the news calmly. Later, the police discuss whether Olaug should be moved to a different location for protection. Waaler argues against moving Sivertsen, saying unusual activity might alert the killer. Beate angrily accuses him of using an innocent woman as bait. Since her only son lives abroad, they decide she will remain in the house. Waaler updates the team that the student building has been outfitted for surveillance and he students have been told to stay in their rooms on Saturday. Later, Harry and Aune (the psychologist) discuss how Harry was able to crack the code, and why the killer has created the elaborate network of code.

Walking home, Harry encounters Vibeke Knutsen (the woman who lives in the flat below Camilla). Harry invites her back to his apartment, where she confides that her fiancé behaves strangely, and that she is unhappy in her relationship. Vibeke propositions Harry, but he rejects her, telling her he wants someone else. She becomes emotional and leaves.