When crime lord Jack Barker's brother is murdered, it is Barker's old friend, DCI Frank Palmer, who is tasked with leading the investigation to find the perpetrator. The gangster's pursuit of vengeance leaves a wake of destruction across the capital and triggers a wave of violence that rapidly engulfs the city's underworld. DCI Palmer attempts to restrain the rampaging Barker as he searches for answers, and soon discovers that old sins have long shadows.