Anna Khitrova, a British-Russian midwife at a London hospital, finds a Russian-language diary on the body of Tatiana, a 14-year-old girl who dies in childbirth. She also finds a card for the Trans-Siberian Restaurant, which is owned by Semyon, an old vor in the Russian mafia. Anna sets out to track down the girl’s family so that she can find a home for the baby girl, and meets with Semyon, who offers to help. Anna’s mother Helen does not discourage her, but Anna’s Russian uncle Stepan, who claims he is a former KGB officer, urges caution. When Stepan translates Tatiana’s diary, Anna comes to learn that Semyon had raped the girl after his son Kirill’s failed attempt to do so (on account of his homosexuality), gotten her addicted to heroin, and forced her into prostitution. Ultimately, Anna realizes that the baby was fathered by Semyon.
Semyon’s driver, Nikolai Luzhin, also serves as the family “cleaner”, removing evidence and dumping murdered bodies in the River Thames. Through Nikolai, Semyon, fearing prosecution, promises to give the location of the girl’s family to Anna if she hands back the diary. Nikolai takes the diary and gives a location, but urges Anna to keep the baby in London. Semyon orders Nikolai to kill Stepan, who soon goes missing. As Nikolai’s star rises within the vory, Semyon sponsors him as a full member, due in part to Nikolai’s protection of Semyon’s playboy son Kirill, who authorized an ill-advised hit on a rival Chechen vory leader with the help of a Turkish associate, Azim, and without Semyon’s approval. Two Chechen hit men soon arrive in London seeking vengeance and kill Azim’s mentally handicapped nephew, who also took part in the hit. Semyon hatches a plan to trick Nikolai into taking Kirill’s place during a meeting at the baths with Azim. The Chechens attack, thinking Nikolai is Kirill, but Nikolai kills them both, ending up in the hospital with severe wounds.
It is revealed that Nikolai is actually an FSB agent who has infiltrated the gang, working under license from the British Government. As part of his undercover duties, Nikolai was able to read Tatiana’s diary before Semyon destroyed it, and hatches a plan with his handler to have Semyon arrested for statutory rape, with a paternity test of Tatiana’s baby as evidence. Nikolai tells Anna that Stepan is safe, in a 5-star hotel in Edinburgh for protection. Semyon orders Kirill to kidnap the baby girl and kill her. However, as Kirill sits by the Thames working up the courage to throw the child in, Nikolai and Anna find him and persuade him to give the baby back. Nikolai and Kirill embrace as Nikolai tells him that his father is finished and they are now the bosses. Nikolai succeeds Semyon as boss of the organization and Anna gains custody of Tatiana’s baby, whom she names Christine.