Line of Duty - Episode Guide

When Steve Arnott is transferred to a police anti-corruption unit, he finds his target is the city's top detective, Tony Gates. Can Gates really be as good as he appears? Arnott must engage in a cat-and-mouse struggle to uncover Gates' secret.

Having been duped into covering up Jackie's crime, Gates is desperate to sever ties with her. But, as Arnott and Fleming close in on his secret, Gates is plunged into an even more dangerous situation than he first thought.

Arnott is convinced Gates played a part in Jackie's disappearance. With Fleming's help, the anti-corruption team tries to trap Gates into revealing his involvement in covering up Jackie's crimes.

Desperate for proof of Gates's corruption, Fleming pushes her relationship with him to the limit. But her behaviour causes Morton to question if she might not be such a loyal colleague after all.

With Gates on the run, the anti-corruption team come under pressure to close the case once and for all. Arnott is forced to make some tough decisions about where his loyalties lie. Fleming and Hastings go all out to catch Gates, leading to a shattering conclusion.

A brutal ambush on a police convoy leaves three officers dead and a protected witness fighting for his life. AC-12 turn their spotlight on Lindsay Denton, the officer who led the convoy but escaped unscathed.

Following the tragedy at the hospital, AC12's Kate Fleming is planted undercover in Lindsay Denton's Missing Persons Unit. But Lindsay in turn gathers compromising evidence against the anti-corruption team.

Lindsay is denied bail and finds herself targeted in prison. Growing increasingly desperate, she tells Kate about a relationship with an executive police officer and her theory of why she is being framed.

Following the violent attack she suffered in prison, Lindsay is granted special dispensation to visit her dying mother. Meanwhile, deputy chief constable Dryden shrugs off allegations about his relationship with Lindsay and possible links to the ambush.

Lindsay fights for her life as troubling details emerge of a vicious conspiracy involving corrupt police officers. With growing evidence of links between DCC Dryden and the ambush, Hastings is under pressure to arrest his senior officer.

AC12's investigation finally exposes a vicious criminal gang run from within the police. But while Steve now appears convinced of Lindsay's innocence, Kate remains determined to prove she had a role in the ambush.

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.

After months of hunting a serial killer, DCI Roz Huntley faces intense pressure to apprehend a suspect. Michael Farmer is caught and charged with the crimes, but doubts about the young man's guilt lead the chief forensic investigator to AC-12.

When DCI Roz Huntley captures a serial killer, Forensic Coordinator Tim Ifield alerts AC-12 to a possible miscarriage of justice.

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. Meanwhile Arnott and Fleming continue to clash.

As shocking new evidence is unearthed, AC-12 step up their investigation in to the case against Michael Farmer. Could the real killer still be at large? Meanwhile, Detective Constable Jamie Desford joins the AC-12 team.

Roz's husband Nick is brought in for questioning by AC-12. But while Nick denies any involvement in Steve's attack, his suspicions about Roz mount. Meanwhile, AC-12 discover new anomalies in the forensic evidence and issue DCI Roz Huntley with a second Reg 15 notice. AC-12's case appears watertight until Roz starts dismantling their evidence with inside information of her own.

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.

The explosive series finale pits AC-12 against Roz in a climactic duel to find Tim's murderer and unmask Balaclava Man.

Following the deadly hijack of a police convoy, AC-12 target a ruthless organised crime group known to have links with corrupt 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.

Corbett's most daring plan yet requires McQueen to exploit links with corrupt police officers. AC-12 make a shocking discovery.

Tensions rise in the OCG following the events at Eastfield. With troubling questions hanging over the identity of 'H', suspicions mount at AC-12.

As the hunt for 'H' intensifies, Steve and Kate wonder if Hastings is guarding a dark secret.

In a nail-biting finale, closely guarded secrets are revealed.

Carmichael's dogged interrogation of Hastings presents mounting evidence of suspicious behavior. Caught in the crossfire, Kate and Steve are torn between loyalty to Hastings and their duty to uncover the truth, however painful. Will the identity of "H" be revealed at last?

When new information comes to light about a possible suspect in a year-long unsolved murder investigation, DCI Joanne Davidson appears keen to finally bring Gail Vella's killer to justice. However, after her conduct arouses suspicions, it's not long before AC-12 are on the case. But as AC-12's investigation uncovers deeper and darker information, will DCI Joanne Davidson turn out to be their most dangerous adversary yet?

Having opened an official inquiry into DCI Jo Davidson and Operation Lighthouse, AC-12 begin to suspect a cover up. Steve and Chloe dig into Gail Vella's controversial reporting for clues to her murder, and find links to previous AC-12 cases. Their investigation takes a shocking turn when they begin to scrutinise Jo's personal life.

On the strength of evidence from a new witness, DCI Jo Davidson brings Terry Boyle back in for questioning about Gail Vella's murder. Kate is torn between loyalty to Jo and wanting to assist AC-12's investigation, and tensions increase when Kate encounters a face from the past with links to organised crime.

DCI Jo Davidson faces increasing pressure from all sides as AC-12 make major breakthroughs in the investigation.

Hastings acknowledges that the disciplinary action against him put Kate and Steve in a difficult position, and a forensic report from Farida's house results in a shock for AC-12.

AC-12 link Gail Vella's murder with a historic case of police corruption, and Kate hatches a plan to tell once and for all if Jo is bent.

They are closer than ever to cracking the case, but when Hastings' authority is undermined it leaves his team in a potentially dangerous situation.

As AC-12 struggle to deal with the repercussions of tragic events, Hastings makes one final bid to uncover institutionalised corruption before his time runs out.

With time running out, AC-12 attempt to unmask 'H', the Fourth Man (or Woman) commanding the network of corrupt officers behind the murder of Gail Vella. But sinister and powerful forces appear intent on orchestrating a cover-up.