It is Thomas Shelby's long-awaited wedding day. In the middle of the celebrations, a mysterious visitor imperils the entire Shelby family, and Tommy finds himself pulled into a web of intrigue more lethal than anything he has yet encountered.
Tommy discovers the extent of the mission given to him and the extreme lengths his new paymasters are willing to go to in their quest for power. Meanwhile his own family's activities lead to escalating danger in Birmingham.
Responding to the Italians' actions, Tommy is set on a path of deadly vengeance that could take him to his darkest place yet, and threatens to splinter the family. Meanwhile, as he makes plans for his mission on behalf of the Russians, he realises there is a traitor in his midst.
Tommy and Tatiana play a personal and dangerous game to acquire information from one another, and Tommy finally comprehends the magnitude of Tatiana's warped ideals. Meanwhile, Polly reveals a dark secret, with terrible consequences for Tommy.