Two years after expanding his empire, Thomas Shelby marries the love of his life, Grace Burgess, and settles into a massive countryside estate with their infant son, Charles. However, his criminal past immediately catches up with him. A corrupt government organization known as the Economic League, led by the ruthless Father John Hughes, forces Tommy into an international conspiracy. He is coerced into smuggling British tanks and weapons to anti-Bolshevik Russian refugees who are fighting the Soviet government.

Tommy aligns with exiled Russian aristocrats, including the unpredictable Grand Duchess Tatiana Petrovna. As payment for his services, the Russians provide Tommy with a hoard of priceless jewels, including a massive sapphire necklace. During a grand charity gala hosted by the Shelbys, Grace wears the sapphire, which Tatiana secretly warns Tommy is cursed. Moments later, a hitman sent by the Italian mobster Vicente Changretta fires into the crowd. The bullet strikes Grace, and she dies in Tommy's arms.

Grace’s death destroys Tommy’s sanity, driving him into absolute darkness and a relentless quest for vengeance. While the Shelby brothers hunt down and brutally eliminate the Changretta family, Tommy discovers that Father Hughes is playing a double game. The priest is secretly leaking information to the Soviet embassy, planning to trigger a train bombing that will force Britain to break diplomatic ties with Russia and declare war.

When Father Hughes realizes Tommy knows his plan, he kidnaps baby Charles to maintain leverage, demanding that Tommy proceed with the train bombing. Trapped, Tommy plans a massive counter-offensive. He orchestrates a heist to tunnel beneath the Russian vault and steal their diamonds before they can flee the country.

On the night of the heist, Michael Gray tracks down Father Hughes to rescue Charles, killing the priest just seconds too late to stop the train explosion. With Charles safe and the Russian jewels successfully stolen, Tommy calls a family meeting to distribute the wealth. But as Polly, Arthur, John, and Michael celebrate, Tommy reveals that the police have surrounded the house. To secure long-term immunity from the government for the train bombing, Tommy has made a secret deal with the British crown, resulting in the immediate arrest of his entire family and leaving him completely alone in his empty empire.

This shocking betrayal completely fragments the tight-knit Shelby clan, breaking the absolute trust that had kept them alive through wars and street battles. As Arthur and John are dragged away in handcuffs alongside Polly, the heavy weight of Tommy's cold calculated nature becomes an unforgiving reality for everyone involved. He watches them leave from the window of his massive estate, fully aware that his actions have saved them from the gallows, even if it means they will hate him forever.

Alone in his dark study, Tommy is left to navigate the dangerous psychological aftermath of losing both his wife and his family's loyalty in the exact same week. The stolen Russian jewels, while vastly increasing the financial reach of Shelby Company Limited, offer zero comfort to a man who now speaks mostly to the ghost of Grace. The empire is larger, the political connections run all the way to the crown, but the foundation is entirely hollowed out.

Meanwhile, behind prison bars, the family's resentment grows deeper with each passing day, setting up a massive ideological rift between Tommy's global ambitions and the street-level loyalty of the original Small Heath gang. Michael Gray begins to see the vulnerability in Tommy's absolute rule, sparking the first hidden embers of a future rebellion within the company.

Outside the prison walls, the political landscape shifts violently as the British government begins utilizing Tommy's unique skill set for even darker operations, ensuring he remains a puppet of the crown. By sacrificing his own flesh and blood to the legal system to win a larger chess match against international powers, Tommy permanently alters his own humanity. He transitions from a ambitious Birmingham gang leader into a cold, isolated political figure who relies entirely on fear rather than family love to maintain his crown.