At Christmastime 1925, members of the fractured Shelby family get word that the New York Mafia is coming to avenge murders they committed a year earlier.
Reeling from their loss, the Shelbys gather in Small Heath, where Tommy calls for a family truce in order to launch an offensive against the Mafia.
Linda tries to distract Arthur, who later gets caught in an ambush; Tommy is reminded of who he was before the war; Polly meets a man from her past.
The Mafia tries to lure one of the Shelbys into a trap; an old flame visits Tommy; Lizzie receives unexpected news.
Despite being outnumbered, Tommy starts a shootout with the Mafia; Luca Changretta approaches Alfie Solomons; the British military seeks out Ada.
During the boxing match, Arthur follows a hunch; words of wisdom from Alfie inspire Tommy, who gets valuable intel from Jessie.