In the first season, Steve Arnott (Martin Compston) is transfered to AC-12, the Anti-Corruption police department. His first assignment is to investigate the city's top detective, DCI Tony Gates (Lennie James), who is involved with a woman named Jackie Laverty (Leanne Best). Gates discovers Jackie has been involved in a hit and run that left her accountant dead, and begins to suspect her of illegal dealings. Meanwhile, several unsolved murders seem to be linked to Gates as well.
In the second season, AC-12 turn the spotlight on DI Lindsay Denton (Keeley Hawes), the officer in charge of a police convoy that was brutally ambushed, leaving three officers dead.
The third season finds AC-12 investigating after a criminal is shot dead by Sergeant Danny Waldron (Daniel Mays) after the evidence suggests it was a deliberate killing rather than self-defense. That leads to the investigation of child abuse at an orphanage years earlier.
The fourth season follows the case of DCI Roz Huntley (Thandie Newton), who takes a young man into custody, believing him to be a serial killer, based on circumstantial evidence. However, Forensic Coordinator Tim Ifield (Jason Watkins) alerts AC-12 to a possible miscarriage of justice.
When three police officers are killed during the hijack of a seized drugs transport, but the fourth is left alive and has a good description of the woman who didn't kill her as she was ordered, the AC-12 moves in to investigate the possibility of an undercover policeman who may have gone rogue.
In the sixth season, Superintendent Ted Hastings (Adrian Dunbar), Detective Inspector Kate Fleming (Vicky McClure) and Detective Sergeant Steve Arnott investigate the suspicious conduct of Detective Chief Inspector Joanne Davidson (Kelly Macdonald) on an unsolved murder case.
|Cast:||Adrian Dunbar, Martin Compston, Vicky McClure, Kelly Macdonald, Craig Parkinson, Aiysha Hart, Keeley Hawes, Polly Walker, Paul Higgins, Owen Teale, Mark Bonnar, Lennie James, Leanne Best, Daniel Mays, Thandiwe Newton, Jason Watkins|
|Director:||Daniel Nettheim, David Caffrey, Douglas Mackinnon, Gareth Bryn, Jed Mercurio, John Strickland, Michael Keillor, Susan Tully|
|Producer(s):||Jed Mercurio, Ken Horn, Peter Norris|