Line Of Duty

The series opens with the violent ambush of a police convoy in which three officers are killed and a protected witness seriously injured. When evidence suggests that a police source may have leaked the whereabouts of the convoy to criminal parties, DCC Mike Dryden (Mark Bonnar) takes personal charge, assigning anti-corruption unit AC12 to the case. With DS Kate Fleming (Vicky McClure) reluctant to join an investigation she has personal links to (she trained with one of the ambush victims) DS Arnott (Martin Compston) and Superintendent Hastings (Adrian Dunbar) are joined by new recruit DC Georgia Trotman (Jessica Raine). Initially AC12's most valuable witness, the suspicion soon arises that the sole surviving police officer, DI Lindsay Denton (Keeley Hawes) could be their prime suspect. Did she lead the convoy straight into the fatal ambush?

AC12 and the Major Violent Crime unit lock horns over the tragedy at the hospital and the evidence surrounding the ambush. Meanwhile Kate (Vicky McClure) continues to work undercover with Lindsay (Keeley Hawes) in Missing Persons. They look into the disappearance of 15-year-old Carly Kirk, a case Lindsay appears personally invested in. She is secretive and volatile as the evidence against her mounts, but it's clear she won't go down without a fight. As Lindsay starts to scrutinize the background of the AC-12 officers, they're forced to go on the defensive - Kate, Steve (Martin Compston) and Hastings (Adrian Dunbar) all have reasons for wanting to keep their private lives under wraps. As public and private pressure on the case reaches frenzied levels, it appears that the team's conduct might compromise the case against Lindsay.

Lindsay Denton (Keeley Hawes) maintains her innocence but is denied bail and sent to prison to await trial. When she's subject to a violent attack inside the prison, she confides in Kate (Vicky McClure) that she had a previous relationship with an executive police officer - who may have reason to want her framed. When AC12 are at last given access to files on the (now deceased) protected witness by Major Violent Crime, the evidence suggests a possible police conspiracy. With cracks starting to show in AC12's case against Lindsay, the cohesion of the team is further threatened by the arrival of former adversary, DI 'Dot' Cottan (Craig Parkinson). Meanwhile the mutilated body of a teenage girl is found buried under a collapsed garage floor: Could this be Carly Kirk, the girl Lindsay was searching for?

While AC-12 are under increasing pressure to indentify the police leak that led to the ambush, Hastings (Adrian Dunbar), Steve (Martin Compston) and Kate (Vicky McClure) have their own demons to battle. Meanwhile, Lindsay insinuates that Deputy Chief Constable Dryden (Mark Bonnar) was embroiled in a wider conspiracy and when AC12 discover video recordings made by the witness while in protective custody, Dryden's guilt is compounded. Then Steve Arnott uncovers evidence that a tracker had been planted on one of the convoy vehicles and it seems that Lindsay (Keeley Hawes) has been telling the truth all along. When she is given special dispensation to visit her dying mother, AC12 realise too late how much danger she may be in.

Lindsay (Keeley Hawes) fights for her life as disturbing details emerge of a conspiracy involving corrupt police officers. Cottan (Craig Parkinson) is tasked with finding the identity of 'The Caddy', the police officer who is the link between the corrupt officers and the criminal underworld. Steve (Martin Compston) uncovers startling new details about Lindsay's relationship with Deputy Chief Constable Dryden (Mark Bonnar) and, despite Kate's (Vicky McClure) protestations, pays attention to Lindsay's theory of why she is being framed. Hastings (Adrian Dunbar) is under pressure to arrest his senior officer as evidence appears to conclusively link Dryden to the ambush.

AC12's investigation exposes a vicious criminal gang run from within the police, aided by 'The Caddy', whose identity Cottan (Craig Parkinson) has apparently uncovered thanks to the help of his former colleague DC Morton (Neil Morrissey). Dryden (Mark Bonnar) is charged with conspiracy to pervert the course of justice, vindicating Hastings' (Adrian Dunbar) brave stance. But while Steve (Martin Compston) now appears convinced of Lindsay's (Keeley Hawes) innocence, his close relationship to the former chief suspect unsettles Kate (Vicky McClure). Despite mounting pressure both at work and home, Kate remains determined to prove Lindsay had a role in the ambush.