A teenage, pregnant girl from Russia stumbles into a pharmacy in London, wearing a trench coat that conceals her severe injuries. As she loses consciousness, she's quickly rushed to Trafalgar Hospital on December 20th. There, Anna Khitrova, a midwife with Russian-British heritage, discovers a diary written in Russian on the body of the deceased girl, Tatiana. The stark reality of Tatiana's bruised body serves as a haunting reminder of the tragedy.
The emergency Cesarean section delivers a healthy baby girl, which Anna is now determined to place into a loving home. In pursuit of this goal, she tracks down the infamous Russian mafia owner, Semyon, who runs the Trans-Siberian Restaurant. Despite Anna's mother's supportive stance, her uncle, Stepan (who has a KGB background), is hesitant; he doubts Tatiana’s character, believing she was involved in prostitution. Having read her diary, Stepan insists she bury it with Tatiana, adding that a mixed-race baby is doomed, referring to Anna's own loss.
Anna confronts Semyon to inquire about Tatiana's life. He feigns ignorance, claiming she never worked at his restaurant but subtly hints he may know more. He alters the course of their interaction by offering his assistance in translating the diary, dismissing Anna's relatives’ abilities in favor of his own. Anna safeguards the original diary, aiming to share it with Tatiana’s daughter in the future.
As the plot thickens, Semyon’s son Kirill (Vincent Cassel) tempts the fate of their world by ordering a reckless hit on a rival Chechen leader, leading to a violent showdown. This decision spirals into chaos, embroiling Nikolai Luzhin — Semyon’s driver and the “cleaner” of messes. While Nikolai expertly navigates the aftermath of the hit, he finds himself drawn to Anna, admiring her unique Ural motorcycle which is no longer manufactured.
Upon Stepan's completion of the diary translation, Anna uncovers the truth: Tatiana was merely a naive girl with dreams of success, lured into a nightmarish reality of sexual exploitation by Semyon and his crew. The shocking revelations force Anna to confront Semyon and negotiate for information about Tatiana's family in exchange for the diary.
But as events unfold, Nikolai receives orders to eliminate Stepan, pushing him further into the mafia underworld. With tension escalating, the Chechens seek retribution, targeting family members associated with the initial murder. Semyon’s empire begins to crumble as betrayals unfold and deadly encounters become unavoidable.
In a twist of fate, authority finally catches up with Semyon through Nikolai’s hidden identity as an undercover agent for the FSB, which he cleverly utilizes to his advantage. Anna learns about the whereabouts of Tatiana's child, finding herself in a crucial race against time to protect the innocent life.
In an emotionally charged climax, Anna, alongside Nikolai, manages to save Tatiana’s baby sister from a horrifying fate, rekindling their hope as they form an unexpected partnership within the shadowy realm of organized crime. With Semyon’s reign ending, Nikolai ascends as the head of the mafia and Anna vows to care for Tatiana’s daughter, naming her Christine. Together, they forge ahead into a treacherous yet promising future.
