Leo and Raisa travel to Moscow under false papers. Raisa reflects that their partnership in the investigation has given her life a purpose beyond mere survival. Their train arrives at Yaroslavskiy Vokzal, where Arkady’s body was found. Their primary objective is locating Galina Shaporina, the eyewitness who saw the killer. Raisa also wants to consult her former colleague, Ivan, who has access to censored Western material on similar crimes, though Leo is wary of involving him.

As the couple navigates the heavily policed station, a state security agent stops them and demands papers. Leo knows the documents Nesterov forged are flawed, but Raisa realizes that the agent is barely literate and maintains a fearful expression to appease him. After a cursory inspection, the agent releases them.

Leo visits Fyodor’s apartment to find Galina Shaporina. Fyodor’s mother opens the door and breaks down when Leo admits that she was right about Arkady’s murder. Leo shows Fyodor and his family the case files detailing over 40 similar murders. When asked what he will do with the killer, Leo says that he will kill him. Fyodor immediately agrees to help.

At Galina’s apartment, Fyodor and Raisa enter while Leo waits outside to avoid frightening her. Nevertheless, Galina is nervous; they explain that they are private citizens investigating linked murders, but she insists that she knows nothing. Her husband appears, followed by curious neighbors. In a final attempt, Raisa hugs Galina and quietly asks for a description, but Galina stays silent.

Six-year-old Nadya sneaks out for a walk along the river Don. She sees a tall man in a coat and glasses carrying a case, recalls her mother’s warning about strangers, and decides to run past him with a polite greeting. The man grabs her, but after a moment’s fear, she realizes that it is her father, Andrei, returning from a work trip.

At home, Nadya steps on the family cat’s paw, disguising her action as an accident. Andrei becomes enraged, grabs her wrist, and warns her never to touch the cat. He descends to his private basement space, removes from his case a sealed glass jar containing the stomach of a girl he murdered hours earlier, cooks it, and feeds it to his six cats. Upstairs, Nadya contemplates killing one of the cats her father prefers to his children.

Having failed with Galina, Leo and Raisa wait in a grocery line to watch for Ivan’s return. Leo reflects on his marriage; he is jealous of Raisa’s longstanding closeness with Ivan but wonders whether their new partnership might grow into genuine love. He and Raisa follow Ivan home after confirming that he is not under surveillance. Inside his well-furnished apartment, Leo shows Ivan the case files. Ivan accuses Leo of setting a trap to regain favor with the MGB, but Raisa insists that the murders are real and that her husband’s change of heart is earnest.

Ivan agrees to help and mentions a retired MGB psychiatrist, Professor Zauzayez, who might profile the killer. As Ivan telephones the professor, Leo notices the apartment’s luxury and realizes that Ivan must be an informant. Leo attacks Ivan, strangling him with the telephone cord. Raisa tries to intervene, unwilling to believe that Ivan is a traitor until she opens a drawer and finds a censored book with a list of names—people Ivan loaned it to in order to incriminate them. Realizing the truth, she turns away as Leo kills him.

Leo and Raisa flee Ivan’s apartment as agents arrive. With no train until morning, Leo decides to risk visiting his parents. They arrive at a dilapidated building and find his parents, Stepan and Anna, sharing a narrow bed in a small, windowless back room.

Leo wakes them silently. He explains that he was demoted and exiled—not killed, as his parents believed—and that his letters to them were likely intercepted. Anna tells him that she is proud of him but that this will be their last meeting. Before Leo and Raisa say their goodbyes, Stepan gives Leo a sealed letter to read on the train, explaining that it contains everything they were never able to say.

On the train back to Voualsk, Leo opens his father’s letter. It begins by saying that his parents have no regrets and that they thought he preferred to forget an unspecified “matter.” Leo stops reading, recognizing what the letter addresses—a past event he has spent his life trying to forget. He tears it into small pieces and throws them out the window.

Nesterov travels by train back to Rostov after visiting Gukovo. He reflects on public rumors about the murders, which include supernatural explanations and a prominent theory that the Nazis left behind soldiers to kill Russian children. He has now counted 57 victims and is convinced that Rostov is the center of the crimes.

He arrives at his mother’s apartment to find his wife, Inessa, beaten, tied, and restrained by a man in uniform. As he rushes forward, the woman from the beach strikes him with a truncheon. The man throws Nesterov’s entire case file onto the floor, and the woman announces his arrest.

Leo and Raisa return to Voualsk and retrieve their buried hiking gear from the forest (they left Voualsk on the pretext of a walking holiday). Aware of the danger they face and the new relationship they have forged, they make love before returning to their room. Slipped under their door is a note from Nesterov instructing Leo to meet him at 9:00 pm in his office, alone, with all documents.

When Leo arrives at militia headquarters, Nesterov urgently explains that he was arrested in Rostov and forced to set a trap for Leo to protect his family. Moscow has branded the investigation anti-Soviet agitation and espionage. Agents will arrive in 15 minutes to arrest Leo, and Raisa is being arrested simultaneously. Nesterov provides an escape plan: Leo will knock him unconscious, hide on the floor below while agents pass, and then escape through a back window to a waiting car. Before time runs out, they deduce that the killer is likely a supply agent traveling between the Rostelmash tractor factory in Rostov and the car assembly plant in Voualsk.

Leo strikes Nesterov unconscious and escapes with the car. However, agents quickly construct barricades to prevent him from leaving town; as he attempts to smash through one, they shoot out his tires, and the car flips and crashes. Leo is dragged from the wreckage to find Vasili standing over him.

Aron, a young militia officer with a cleft palate, is on a stakeout watching a bus shelter for unusual activity. He observes a teenage sex worker approach a tall man in glasses carrying a case—Andrei. After they reach an agreement, they walk toward the trees where Aron is hiding. Aron stops them, checks the man’s papers, and inspects his case. He finds a long serrated knife, which Andrei claims is for cutting salami, and an empty sealed glass jar that Andrei claims is for work samples. Andrei shows his party card and a family photograph, and Aron, viewing him as a decent citizen “corrupted” by the girl, is about to release him when he finds a folded newspaper clipping in the case. Andrei testily asks that he return the photo. Aron is confused by his urgency but sees that the clipping features a wartime propaganda photograph of a triumphant Russian soldier standing over a destroyed tank and dead German soldiers.

Leo is in an interrogation cell in the Lubyanka, injured and secured to a chair. Doctor Zarubin tends to his wounds, enters Raisa’s adjacent cell, opens a grate between the rooms, and begins molesting her. Vasili enters, dismisses Zarubin, closes the grate, and tells Raisa that it would be better to cooperate. She agrees to tell him everything.

Vasili enters Leo’s cell and briefly opens the grate so that Leo can hear Raisa confirm that she is alive. Leo offers to confess to anything, but Vasili says that he already has everything from Nesterov and Raisa. He asks only why Leo pursued the investigation, and Leo realizes that it is not the killing of children that Vasili refuses to accept as real; rather, he genuinely cannot understand why anyone would kill children without political or material motive. Concluding that Leo is experiencing delusions and giving in to personal vendetta, Vasili has him injected with camphor oil, inducing a violent seizure. When it subsides, Vasili asks Leo his name. Leo’s response is “Pavel.”

Leo relives a repressed childhood memory. He sees himself as a boy in a winter forest with another boy, Andrei. He is struck and abducted, waking inside a grain sack with a head wound. He is emptied onto a farmhouse floor where young Stepan and Anna mourn their dead son, whose name was Leo. Questioned, Pavel cannot remember his name or home.

Anna obliquely explains that Stepan intended to kill Pavel to provide food for their son. However, since their son has died, Pavel is free. Stepan and Anna offer him stew made from their son’s body and invite him to come with them to Moscow to seek refuge with relatives; otherwise, he can attempt to return home. With no memory or identity, Pavel agrees to go. When asked his name, he answers with the only name he remembers: Leo.

Raisa is processed through a prisoner station and taken to a hidden platform at Kazan Station, where thousands are being packed into cattle cars. Vasili appears leading a frail, aged Leo. Raisa is shocked by his transformation, but he recognizes her. Vasili, finding his triumph unexpectedly hollow, tells Raisa that he is allowing them to travel to the Gulag together as an act of generosity. A guard shoves them onto the train as the last prisoners to board. On the platform, Vasili confirms with the guard that arrangements have been made for Leo and Raisa to be killed during the journey.