Line of Duty is a police procedural drama series revolving around the investigations of Anti-Corruption Unit 12, a division of the fictional Central Police Constabulary, and their efforts to root out corrupt police officers and clean up the force. The show has been running on TheBBC since 2012; Series 1-3 aired initially on BBC Two, and after the significant success of the third series, it was moved onto BBC One, and has remained there since.
Unmarked spoilers are present throughout the episode pages as well as the synopses below. Tread lightly if you haven't seen certain series or episodes.
DS Steve Arnott is running a counter-terrorism op, when he's given the dreaded Fahrenheit order. His team go into the target's flat and shoot on sight. When the dust clears, the terrible truth is revealed: they entered the wrong flat. Their commanding officer, CI Phil Osborne, tells them to cover it up, and Arnott isn't having it. He's transferred to AC-12, which is currently investigating officer-of-the-year, DCI Tony Gates, over possible laddering. The investigation soon takes on a darker turn when Gates tries to cover up a hit and run by old acquaintance Jackie Laverty, and her bosses get involved.
- "A Disastrous Affair": DS Steve Arnott is transferred to AC-12 after the shooting of Karim Ali. He joins the investigation into DCI Tony Gates, while Gates covers up a hit and run by Jackie Laverty.
- "The Assault": AC-12's investigation turns to the hit and run Gates tried to cover up. Gates makes a troubling discovery about the identity of the victim, and what it means about Jackie.
- "In The Trap": Gates rushes to hide his involvement in Jackie's disappearance, while Arnott dogmatically chases after any evidence tying them together.
- "Terror": AC-12 tries to link Gates to the Greek Lane murders. Gates is pressed into service for mysterious crime lord 'Tommy', and tries to find Jackie's body.
- "The Probation": Gates unites with AC-12 to bring in the man behind the Greek Lane murders, Wesley Duke and Jackie Laverty, the enigmatic 'Tommy'.
DI Lindsay Denton accepts a call from DS Jane Akers asking for secure transport of a witness, and she's soon on her way. However, halfway to the station, her convoy is is attacked by men in black biker leathers; they ram her off the road and kill the three other police officers in the second car, before setting fire to it and burning the witness. AC-12 soon opens an investigation into possible collusion between Denton and the convoy's attackers. The investigation grows and grows as the truth unravels, and soon DCC Mike Dryden is in their crosshairs, while the true mastermind, known only by the pseudonym "The Caddy", pulls strings behind the curtains of AC-12.
- "The Ambush": DI Lindsay Denton comes under investigation from AC-12 after she alone survives an ambush on a convoy carrying a protected witness. AC-12 meanwhile try to deal with blocks on information that might prove or disprove her guilt, and show the ropes to new recruit Georgia Trotman.
- "Carly": Trotman's defenestration galvanises AC-12 against Denton; she does her own digging into them, while taking on the Missing Persons case of a teenage girl called Carly Kirk.
- "Behind Bars": Denton tries to survive prison life, under constant assault for talking to AC12. They, meanwhile, find new evidence implicating DCC Mike Dryden.
- "Blood Money": The investigation turns to Richard Akers, who reveals Jane was on the take. Evidence implicating Dryden grows, while Denton gets a taste of freedom.
- "Last Words": Denton gets the drop on her captors and forces a confession from one. AC12 arrest DCC Dryden and question him, and Denton is released on bail.
- "The Caddy": Arnott does an undercover op on Denton, while she recalls the events that led to her agreeing to hand over Tommy Hunter to his associates.
Sergeant Danny Waldron and his team of AFOs, Rod Kennedy, Jackie Brickford and Harinderpal "Hari" Bains, are on an op to stop a target from committing a gangland execution. When they catch up to the target, though, Waldron runs ahead and, while his team are arming themselves, shoots the target three times in the head after he's disarmed himself. He immediately stages a cover-up, and AC12 get involved, smelling pre-meditated murder. Waldron's own death soon after, though, sets them on the trail of a selection of high-level police officers implicated in historic sex abuse, and The Caddy grows increasingly desperate in his attempts to keep AC-12 from finding out his employers.
- "Monsters": Sergeant Danny Waldron kills a defenceless man, then conspires to cover it up with his team. He starts leaving a trail for AC-12 to follow after they open an investigation into him, but this gets The Caddy's attention.
- "The Process": Stress mounts as Rod, Jackie and Hari come under intense scrutiny following Waldron's death in their presence. Denton's bail proceedings begin.
- "Snake Pit": The cover-up collapses with the death of Rod Kennedy, and The Caddy sets up Hari for his murder. Denton is released on license.
- "Negative Pressure": Denton's release splinters AC-12, and Dot takes the opportunity to set up Arnott as The Caddy.
- "The List": Arnott, suspended from duty, joins with Denton to search for Danny Waldron's list. Dot rushes to stay ahead of them, while further implicating Steve.
- "Breach": Steve is arrested and interviewed following Denton's murder. The tables are turned on Dot, and The Caddy is exposed.
A woman is abducted by a man in a balaclava, but he bungles it and gets noticed. The officers working on Operation Trapdoor, led by DCI Roz Huntley, identify his car at the house of Michael Farmer, where they find the woman, Hana Reznikova, chained up alongside trophies of other kidnapped girls. Farmer is arrested for the abduction and the murders of two other girls, Baswinder Kaur and Leonie Collersdale, but forensic scientist Tim Ifield soon has doubts about the evidence linking Farmer to the victims; he goes to AC-12 with concerns that evidence exonerating Farmer is being ignored by Huntley to get a quick conviction. The investigation is slow-going, until Ifield's murder sets off a chain of cover-ups and lies to protect the career of Roz Huntley, which sees everyone questioning what the truth really is. This eventually brings out the key players behind the Gates case, and sets AC-12 on the path towards rooting out the bent cops that colluded with Tommy Hunter and put The Caddy on their force.
- "In The Shadow Of The Truth": Michael Farmer is arrested for the murders of two girls, but forensic scientist Tim Ifield raises concerns about his guilt to AC-12. Steve tries to build a case against SIO DCI Roz Huntley, and Kate is planted on her team.
- "Who Sows The Wind": Suspicions grow; Roz Huntley is missing, and 5 days after she reports in, Ifield is found dead in a suspiciously clean flat. Huntley rushes to cover up her visit there, tampering with evidence, and tries to hide a strange graze on her wrist. She's recused from Operation Trapdoor, and Ian Buckells is installed in her place. Tim becomes the prime suspect for Balaclava Man.
- "In The Trap": AC-12 learn of Ifield's activities on the night of his death; their suspicions turn to Nick Huntley, whose own whereabouts on the night of Tim's death are unknown. A witness identifies Farmer as a sexual harasser. New hire Jamie Desford is brought on as Steve's partner. Steve is assaulted at Nick's office.
- "Moral Superiority": Nick Huntley is interviewed over Steve's assault, and manages to answer their questions. Steve is hospitalised. With the finding of new CCTV footage, AC-12's prime suspect for Balaclava Man becomes Mr Huntley. He reveals to his wife that he went to Ifield's flat on the night of his murder. AC-12 reinterview Roz Huntley, and she turns the tables on them using information supplied by ACC Hilton.
- "Lying Nest": Hilton recuses AC-12 from the investigation into Roz Huntley, while Nick grows increasingly suspicious of her actions on the night of Ifield's murder. Her wound turns septicaemic, and her hand is amputated to save her life. AC-12 turn their attention to Nick's solicitor, James Lakewell, who previously represented Farmer and so could have told Roz to target him. Jamie transfers from AC-12 after his login is used to access Cottan's Dying Declaration. Roz arrests her husband to save herself, and Hilton serves Ted a Reg 15.
- "Royal Hunting Ground": Nick is interviewed by Murder Squad regarding his involvement in Tim's murder. AC-12 uses information divulged in these interviews to retrace Roz's steps in the nights after the murder to find evidence that can link her to it. Roz investigates Lakewell with Jodie's help. AC-12 bring Roz in for one last interview, and she confesses to accidentally killing Tim. She outs Lakewell and Hilton as links between police and organised crime, responsible for Steve's injury. An attempt on Lakewell's life is prevented. Hilton is killed for his silence.
After an Organised Crime Group attacks and burglarises a transport of drugs, ED 905, leaving all but one officer dead, AC-12 is brought in to investigate possible police collusion to engineer the ambush. Their investigation soon leads them to Operation Peartree, the aim of which is to embed an undercover officer in the same crime group that they're investigating. So starts a game of cat and mouse as AC-12 chase the undercover officer, DS John Corbett, but they are being betrayed from within. Is it Arnott, who feels sympathetic to Corbett's true goal of unmasking the enigmatic "H"? Is it Hastings, who is acting increasingly erratically and making unexplained visits to OCG members? Is it someone as yet unseen? As Corbett goes further and further beyond the line between right and wrong, links start to appear between his own investigation into H and Supt. Hastings' past in the Royal Ulster Constabulary.
- "Episode 1": Jane Cafferty is the sole survivor of an ambush on a convoy transporting drugs for incineration. AC12 opens an investigation into the ambush, and soon discovers an undercover op, which has an officer embedded in the ambushers.
- "Episode 2": An AC-12 officer is dead, and the investigation into the OCG gathers pace. Corbett raids a shipment of assault rifles, and makes contact with Arnott.
- "Episode 3": The OCG raids the high-value Eastfield Depot, engineered by Corbett to bring H out of the woodwork. Arnott severs their collaboration.
- "Episode 4": Tensions and suspicions mount in the OCG, as they struggle to offload the takings from Eastfield, and in AC12, as evidence increasingly points to Hastings' guilt.
- "Episode 5": AC-12 is taken off the investigation into Peartree, and suspicion around Hastings reaches boiling point as he lies and breaks protocol to bring in what remains of the OCG.
- "Episode 6": AC-3 is brought in to investigate and interview Hastings after Steve and Kate's complaint to DCC Wise. While they cross the country hunting the origins of Peartree, Hastings fights for his life against a mountain of evidence.
It's been a year and a half since the Peartree inquiry. Kate has transferred to the Murder Investigation Team at Hillside Lane, Ted is being locked out of meetings with senior officers, and Steve is talking with Nicola "Jolly" Rogerson about transferring to Serious and Organised Crime. Everyone's loyalties get tested, however, when Kate's new squad becomes the subject of an AC-12 inquiry. Kate's boss, DCI Joanne Davidson, is SIO on the murder of controversial journalist Gail Vella on September 10th, 2019. Another DS on the squad, Farida Jatri, becomes suspicious when Davidson seemingly unnecessarily delays an operation to arrest the only suspect they've ever had for the murder to attend an armed robbery - a robbery that no-one else saw any hint of until it happened. The AC-12 inquiry struggles to make headway - there's no identifiable motive for her murder in her material, and Davidson is obsessively throwing her colleagues under the bus to save herself - until Ryan Pilkington is mysteriously seconded onto the squad. Soon after, Steve comes under investigation from Occupational Health over his painkiller usage, and Ted is given a deadline to retire; on CC Osborne's orders, AC-12 is being cut back and merged with the other Anti-Corruption units. Now with a ticking clock to close the inquiry and find Vella's killer, tensions are high. Those tensions become taut when "H", now "The Fourth Man", resurfaces. This is AC-12's biggest-ever inquiry, but will Steve, Kate and Ted see the end of it?
- "Episode 1": MIT receive new intel on a suspect in Gail Vella's murder, and after a delay, DCI Jo Davidson authorises an op to arrest them. En route, Davidson orders them to attend an armed robbery, further delaying the op. By the time they get there, they find Terry Boyle. PS Farida Jatri reports her concerns to AC-12, and Steve fights to get an inquiry authorised.
- "Episode 2": AC-12 is now actively investigating Operation Lighthouse. Jo now has to contend with that and the newly-seconded Ryan Pilkington. Ted comes in conflict with DCC Wise and PCC Sindwhani. Before long, Davidson's in AC-12's interview room, and their suspicion turns to PS Jatri, whose prints are all over a set of burner phones found at her house.
- "Episode 3": Pilkington botches an assassination of Terry Boyle, and Kate finally caves and goes to AC-12 for help. Steve recognises him instantly, and they soon put up surveillance on him. At MIT, suspicion turns to DSU Buckells, who was reportedly responsible for Ryan's secondment, and is now putting him forward for a commendation.
- "Episode 4": It's Buckells' turn in the glass box at AC-12, but they glean nothing from him. Steve finally identifies the man in Vella's audio file as James Lakewell, the lawyer who represented the Huntleys in 2017. He stages an op to get Lakewell out of prison and into a situation where he can talk, but the convoy is ambushed. Evidence found at a search of Jatri's house implicates Jo, and highlights her blood relation to a criminal previously known to AC-12.
- "Episode 5": AC-12 stages a sting on MIT with Kate's help, and as they check out potential OCG workshops, AC-12 spy Ryan making a call on a burner phone. Ted, now facing forced retirement, encourages them to maintain surveillance on Ryan. Jo comes under increasing pressure from Pilkington and the Unknown User to get rid of Kate. DCS Carmichael takes over as head of AC-12. New evidence links the murder of Gail Vella to the death in custody of Lawrence Christopher in 2003.
- "Episode 6": Kate and Jo flee the scene of Ryan's murder, and Jo tries to prove she's not bent. AC-12, under Carmichael, find them and arrest them. Jo does another interview in the glass box, where she reveals the truth of her upbringing, her torment at the hands of her father Tommy Hunter, and her role in framing Jatri and Buckells. She's charged and sent to the VPU at Brentiss Prison. Marcus Thurwell is found dead at his home in Spain.
- "Episode 7": AC-12 intercept OCG's communications, and are able to stop an ambush on a prison transport carrying Jo to Hillside Lane. New evidence found by Cybercrime identifies "H", and they bring him in for interview. Ian Buckells has been living a double life, playing the fool while on duty, but secretly managing communications between the disparate OCGs. Steve and Kate heal their relationship and finally accept medical help. Jo enters Witness Protection.
