December 1925. Tommy Shelby OBE has acquired unprecedented legitimacy. The former gangster is also a man alone, estranged from his family and focused only on business. But when he receives a mysterious letter on Christmas Eve, Tommy realises that the Shelbys are in danger of annihilation.

As the enemy closes in, Tommy flees his country house and returns to the only safe place he knows: Small Heath, Birmingham, the slum where he grew up. Facing a more determined and sophisticated threat than ever before, the Shelby family must find a way to put differences aside, work together, take up arms and fight for survival.

As the Shelbys come to terms with the shocking events of Christmas Day, Tommy endeavours to unite his family. Until the current threat is dealt with, their only safe place is together in Small Heath. Johnny Dogs and Charlie set about arming the locals - everyone is now a Peaky bodyguard. Tommy enlists the help of tough Romany Gypsy Aberama Gold, who wants something unusual in return.

Jessie Eden confronts Tommy about the workers' pay. She warns him that revolution is in the air, and when Tommy doesn't relent she calls his bluff. As the situation plays out, Tommy's factory manager tells him he has one more meeting - with a mysterious businessman from Paris. But what transpires is no ordinary meeting with no ordinary businessman.

The Italians launch another attack on the Peaky Blinders. Tommy realises that the Shelbys need to evolve if they are to survive, but some of the family are reluctant to part with tradition.

As the strike takes hold at the Lanchester factory, Tommy pays a personal visit to Jessie Eden, but he is outmanoeuvred when she reveals something she knows about his past.

Changretta plots to continue the vendetta in the most devastating way possible. As well as identifying an enemy of the Shelby family who could help him, Luca makes direct contact with someone at the heart of the Peaky Blinders organisation.

The Peaky Blinders are lured by the Italians into a cat-and-mouse chase on the streets of Birmingham, where it becomes clear that Tommy has met his match. Trapped in Small Heath, Tommy tries to console himself with a visit from an old flame but it soon becomes clear that he can't always get what he wants.

As his factory lies idle, Tommy confronts the possibility that the Communists might win and he will be deemed a traitor to his class. Meanwhile, Changretta prepares to spring another trap.

Tommy finds himself engaged in bloody battle with Luca Changretta and his gang. The family gather to find out what happened, but Lizzie has even greater news to break.

Meanwhile, an army colonel has questions for Ada about her past as a communist, and Jessie Eden confirms just how far she is prepared to go in pursuit of her cause. And sensing an opportunity to capitalise on his situation, Luca Changretta makes his way to London to present a plan to Alfie Solomons.

It is the night of the big fight - Bonnie Gold versus Goliath. But as the bell rings and the crowd goes wild, dangers lurk in the shadows for Tommy Shelby and his family.

When Changretta plays his final ace, he sets in motion a series of events that will change the Peaky Blinders forever.