Line of Duty

A hardened criminal is shot dead by an armed-response unit led by Sgt Danny Waldron, who claims they were acting in self-defence. But when AC-12 gather evidence suggesting it was a deliberate killing, DC Kate Fleming is sent undercover into Danny's team to find out more. She is quick to identify tensions within the team - only for her own conduct to come under scrutiny.

The shooting at the drugs house intensifies the scrutiny on Danny's team, who once again close ranks. But with DC Kate Fleming on the inside, AC-12 feed in new information that helps her expose cracks in the team's story. DS Steve Arnott looks deeper into Danny Waldron's background and makes a shocking discovery. However, Arnott's life is complicated by an investigation into his own past conduct, but - determined to vindicate himself - Steve prioritises his leads into the Danny Waldron case. The increasing pressure on Danny's team pushes Danny's colleague Rod to the edge.

Undeterred by recent events, DS Steve Arnott continues to find crucial evidence in the Danny Waldron case, and when his theory is confirmed he vows to get justice. DC Kate Fleming discovers that PC Hari Bains is making secret calls to an unregistered phone number while having clandestine meetings with his colleague PC Jackie Brickford. With AC-12's suspicions raised, Steve acts fast - but it is DI Dot Cottan's actions that garner praise.

Fresh testimony launches AC-12 back on the trail of the Caddy, a corrupt officer with links to organized crime. But new disturbing evidence suggests the Caddy may reside within AC-12.

Following new evidence obtained by DC Kate Fleming, the former Head of Vice Patrick Fairbank is questioned by AC-12, but despite Kate's best she is left frustrated. Worried by Arnott's contact with Lindsay Denton, DI Dot Cottan takes matters into his own hands, with shattering consequences. Under pressure from AC-12 legal counsel Gill Biggeloe, Ted Hastings has no choice but to make a dramatic and heartbreaking decision.

DS Steve Arnott is arrested on suspicion of murder but continues to protest his innocence. Does DC Kate Fleming's undercover operation hold the key to Steve's guilt and the identity of the Caddy? AC-12 legal counsel Gill Biggeloe pressurises Superintendent Ted Hastings but some new evidence leaves the enquiry turning on its head.