DS Steve Arnott is transferred to the police anti-corruption unit after the death of a man in a mistaken shooting during a counter-terrorist operation.
Martin Compston / Vicky McClure / Adrian Dunbar / Craig Parkinson / Chrissie Harris / Keeley Hawes / Neil Morrissey / Mark Bonnar / Ash Cook
Corbett's most daring plan yet requires McQueen to exploit links with corrupt police officers.
A fresh police leak enables another audacious raid, Arnott's attempts to gather information put him in a dangerous situation, and the team tries to contact the undercover officer.
Following the deadly hijack of a police convoy, AC-12 target a ruthless organised crime group known to have links with corrupt officers.
AC-12 pit their wits against Roz Huntley in a climactic duel to find Tim Ifield's murderer and unmask Balaclava Man.
AC-12's future hangs in the balance after Hilton bars them from investigating Roz Huntley. But Roz's problems are building closer to home.
Following shocking events, AC-12's investigation intensifies. The discovery of new forensic anomalies appears to provide them with a major breakthrough. Meanwhile, Nick Huntley comes under scrutiny.
As shocking new evidence is unearthed, AC-12 step up their investigation in to the case against Farmer. Could the real killer still be at large?
A dismembered body is discovered, and worries grow when Roz fails to report for duty. After further questioning of Michael Farmer unearths crucial new information, AC-12 challenge the case against him.
When DCI Roz Huntley captures a serial killer, Forensic Coordinator Tim Ifield alerts AC-12 to a possible miscarriage of justice.
DS Steve Arnott is arrested on suspicion of murder but continues to protest his innocence. DC Kate Fleming's undercover operation unveils unexpected facts, but will it hold the key to Steve's innocence and the identity of the Caddy?
Waldron's armed-response unit come under increasing scrutiny and again close ranks. But AC-12 feed new information to Kate that helps uncover cracks in their story. Arnott makes a shocking discovery, then his own past catches up with him.
When a criminal is shot dead by a police armed-response unit led by Sgt Danny Waldron, AC-12 gather evidence suggesting it was a deliberate killing rather than self-defence.