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 thus sets out to track down the girl's family so that she can find a home for the baby girl, having meetings with Semyon, whom she initially regards as friendly. Anna's mother Helen does not discourage her, but Anna's Russian uncle and self-described former KGB officer, Stepan, whom Anna asks for help with the translation of the diary, urges caution. Through translation of the diary, Anna comes to learn that Semyon and his ignorant, unstable son Kirill had abused the girl, addicted her to heroin, forced her into prostitution, and raped her. Ultimately, Anna realizes that the baby was fathered by Semyon (in several scenes it is made clear that Kirill is impotent and never had sex with Tatiana).Kirill's driver is Nikolai Luzhin, who also serves as the family "cleaner", 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 but does not give a location, instead urging Anna to keep the baby in London. Semyon distrusts Anna's uncle Stepan and orders Nikolai to kill him. Nikolai accepts and soon Stepan goes missing. As Nikolai's star rises within the vory, an impressed Semyon sponsors him as a full member, due in part to Nikolai's protection of Semyon's incompetent son, who authorized a hit on a rival Chechen vory leader with the help of a Kurdish associate, Azim. The hit was ill-advised and not approved by Semyon. Two Chechen hitmen 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 temporarily 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 by the British Government and a senior police officer. As part of his undercover duties, Nikolai was able to read Tatiana's diary before Semyon destroyed it and hatched a plan to have Semyon arrested for statutory rape, with a paternity test of Tatiana's baby as evidence. Stepan is also safe, hiding in a 5-star hotel in Edinburgh for protection. Semyon orders Kirill to kidnap the baby girl and kill her. But 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 and Anna kiss and part for the last time. Nikolai succeeds Semyon as boss of the organization and Anna gains custody of Tatiana's baby, whom she names Christine.
Output: Question: When two Chechen hitmen arrive in London, seeking vengeance, who do they kill?, Answer: Azim's mentally handicapped nephew.