Set in 1924, two years after the events of Series 2, it follows the Shelby family as they enter a dangerous world of international intrigue. Thomas Shelby and his entire organization are at risk, forcing him to question everything about his ambitions and desires.
It is Thomas Shelby's long-awaited wedding day. 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.