Line of Duty: Everything that happened in series four

By 2017, Jed Mercurio's crime drama Line of Duty was really started to get noticed, with bosses deciding to move the show to BBC One thanks to incredible viewing figures for sister station, BBC Two. As the show got bigger, so did the storylines and budget, with bosses signing up actress Thandie Newton to play the lead role in series four.

Line of Duty is now returning for a seventh series, so whilst we await any more news of the plot, here's your ultimate recap of series four.

What happened in Line of Duty season four?

The fourth series begins with yet another high-octane scene, as a young girl called Hana Reznikova is abducted by a man in a balaclava as she attempts to run for her bus. As bystanders watch the crime unfold from a local café window, the police are called, resulting in DCI Roz Huntley being alerted whilst cooking dinner for her two children.

Under the impression the latest abduction is linked to a suspected serial killer known as 'Balaclava Man', DCI Huntley's team find the abandoned car, before an explosion in a house alerts the team to Reznikova being trapped inside, handcuffed to a radiator.

After saving Reznikova from the burning building, DCI Huntley sets up 'Operation Trapdoor' in order to find the suspect, and it's clear to see she's being put under immense pressure to deliver by ACC Derek Hilton. The team go on to arrest a man called Michael Farmer, who is a convicted sex offender. DCI Huntley is keen to dismiss Forensic Coordinator Tim Ifield's discrepancies that could prove the suspect's innocence, leading him to think she's keen to frame Farmer in order to please her boss.

Worried about the professionalism from DCI Huntley, Ifield alerts AC-12 to a possible miscarriage of justice, revealing to DS Steve Arnott that he believes DCI Huntley is deliberately ignoring forensic evidence, whilst DS Kate Fleming watches the interview in a different room. Taking on board Ifield's concerns, AC-12 leader Superintendent Ted Hastings deploys DS Kate Fleming to go undercover in DCI Huntley's team, with DS Fleming setting up an interview with charged prisoner Michael Farmer.

Later on in episode one, Ifield visits Reznikova in a café she's working in and invites her round to his flat in order to carry out her cleaning services at his property. After DC Jodie Taylor alerts DCI Huntley that Ifield was the last person to look at the forensic reports, she becomes suspicious he's been speaking to AC-12, thanks to a previous visit from DS Arnott, and decides to turn up at his door.

Ifield is quick to admit his suspicions about the case and the pair begin to argue, which causes Ifield to burn his hand on a hot pan, resulting in him slapping her. DCI Huntley goes on to accuse Ifield of assaulting a police office, before he pushes her, resulting in her hitting her head off the corner of the kitchen bench. With blood gushing out the back of her head, Ifield seemingly thinks he's killed her, rushing off to a hardware store to buy tools to dispose of her body. However, in a big twist at the end of the first episode, DCI Huntley wakes up, just as Ifield is about to cut up her body with a chainsaw.

Episode two begins with DCI Huntley's team concerned about her whereabouts, as she fails to show up for work. Farmer is once again interviewed by DS Fleming, where he informs her he was in hospital during the murder of Leonie Collersdale, leading AC-12 to become more suspicious about the real truth.

DCI Huntley finally shows up to work, informing her team she had a 'grim night' after picking up a bug, and she's quickly summoned into ACC Hilton's office, where he informs her she's been served a Regulation-15 Notice by AC-12.

Later in the episode, DCI Huntley is pulled in for questioning by AC-12, where they express their concerns about the forensic evidence surrounding Hana Reznikova. As Superintendent Hastings and DS Arnott push and explain how it would be impossible for Farmer to carry out the attacks, DCI Huntley remains calm and thanks AC-12 for the 'new information'. Not falling for her tricks, Superintendent Hastings reveals to her he's going to recommend a new senior investigator is brought in for Operation Trapdoor, and that DCI Huntley is re-assigned. It's later announced that DCI Ian Buckells will be the new lead of the operation.

When Ifield doesn't respond to a number of DS Arnott's calls and fails to show up to work, he goes to visit him at his flat, where he later forces entry when suspicions arise. As DS Arnott enters the flat with a number of officers, he finds Ifield's body, with three of his fingers amputated. Despite DS Arnott being in control, DCI Huntley quickly shows up and takes charge of the crime scene, much to the fury of DS Arnott. During a forensic investigation of Ifield's flat, DCI Huntley notices her blood splatter on the kitchen counter, leading her to take a sample of Ifield's blood and replace the evidence.

Upon learning that Ifield was wearing a forensic suit when he died, DS Arnott is convinced DCI Huntley murdered him, and with suspicious high, DCI Huntley fiddles with more evidence, inserting a sample of Ifield's blood into evidence for Collersdale's murder, in an attempt to convince ACC Hilton that the murders are connected.

Episode three begins with DCI Huntley calling a joint team briefing for 'Operation Trapdoor' and the murder of Ifield, but she's quick to exclude DS Fleming from the meetings.

DS Arnott persuades Superintendent Hastings to open a full investigation into the murder of Tim Ifield, which results in AC-12 forcibly seizing evidence at DCI Huntley's office. Upon finding CCTV footage of Ifield wearing a balaclava whilst purchasing cutting tools, many believe he could be 'Balaclava Man', but DS Arnott comes up with a theory that DCI Huntley was the one to kill Ifield after her phone history proves suspicious. In attempt to gain more evidence, DS Arnott questions DCI Huntley's husband Nick, asking about her whereabouts and behaviour the night of Ifield's murder.

DCI Huntley interviews Reznikova once more and she admits to being a prostitute and sleeping with Ifield, after texts were found on her phone. Following the interview, DCI Huntley arrests Reznikova for the murder of Ifield, something she profusely denies.

DC Jamie Desford joins AC-12 and is assigned to assist DS Arnott with his investigation. DS Arnott goes back to visit Nick after failing to hear back from him, but after missing messages from his AC-12 colleagues, which informed him Nick's car was seen in the area of Ifield's flat on the night of his murder, DS Arnott is attacked by a man wearing a balaclavas and is thrown down the stairs.

Following the nasty attack, which left DS Arnott badly injured and in hospital, Nick is arrested and pulled in for questioning by AC-12, but denies attacking him and fails to explain why his car was located near Ifield's flat. As tensions rise, Nick's solicitor Jimmy Lakewell gets him released from custody. During a conversation with his wife, Nick informs DCI Huntley he followed her on the night of Ifield's death, meaning he knows of her visit to his flat.

Elsewhere, the cut on her wrist she suffered during the night of Ifield's murder begins to get more painful, resulting in a hospital visit for DCI Huntley, which leads the doctor to take a blood sample.

At the end of episode four, AC-12 find an anomaly in the second forensic examination of the blood spatter which was taken from Ifield's flat - traces of fibres from a forensic over suit. Following the findings, DCI Huntley is questioned once again by AC-12, leading Superintendent Hastings to recommend she's fully suspended from duty. Following this, DCI Huntley accuses Superintendent Hastings of sexism and reveals she's aware that DS Fleming has been acting as an undercover officer in her team.

DCI Huntley goes to ACC Hilton for help, which results in him brandishing a supporting letter and recusing AC-12 from their inquiry. However, after the pair meet up again in a bar, ACC Huntley makes a sexual advance towards DCI Huntley, something she turns down, saying she loves her husband and children.

At the end of episode four, PC Maneet Bindra meets ACC Hilton in a dark alley, handing him a file.

Episode five begins with Superintendent Hastings awaiting the arrival of ACC Hilton, where the pair argue over the conflicting investigations. ACC Hilton later demands DI Cottan's dying declaration, which Superintendent Hastings refuses to provide and defend his team. At the end of their chat, ACC Hilton confirms he's going report him to the Chief Constable and that AC-12 is more damaging to the police service than the officers they are investigating.

DS Arnott begins rehab for his injuries and he's told he may never regain full mobility in his legs.

Biometric findings suggest that the Balaclava Man who attacked DS Arnott and the one seen in the area of Collersdale's murder could be the same man, meaning it couldn't be Farmer, giving DCI Huntley more ammunition to frame Reznikova.

Following the failure of DS Fleming's undercover mission, AC-12 begin to suspect new officer DC Desford could be a mole, leading to Superintendent Hastings accusing him of accessing DI Cottan's dying declaration. Although he's quick to claim he is being scapegoated and denies the allegations, he admits he doesn't want to be somewhere he's not wanted and requests a transfer.

Despite still being in a wheelchair, DS Arnott returns to work and he's quick to discover that Farmer's solicitor was in fact Jimmy Lakewell. After more of Collersdale's body parts are found, further forensic findings reveal the body parts were frozen and buried after Ifield's murder, meaning Farmer couldn't be the suspect. Remembering an old case, DS Arnott recalls that Jackie Laverty's body was cut up and frozen, as well as men in balaclavas also being involved in that attack.

Things go from bad to worse for DCI Huntley as she faints and has her hand amputated due to MRSA, sustained following the cut to her wrist. Despite this, she's quick to go on to frame her husband Nick for Ifield's murder, resulting in her arresting him. Upon questioning, Nick tells the police it was in fact DCI Huntley who murdered Ifield.

At the end of the penultimate episode, ACC Hilton gets his hands on DI Cottan's dying declaration, where he hears DI Cottan saying the corrupt official had a name beginning with 'H'. Much to his shock, ACC Hilton then accuses Superintendent Hastings as being 'H'.

With the understanding that DCI Huntley framed her husband Nick for Ifield's murder, AC-12 narrow their search, with DS Arnott working out she wouldn't have had a lot of time to hide any evidence after the murder. AC-12 go on to do a deep search of the woodland area near Ifield's flat, where they find incriminating evidence. This evidence, along with the fact that the MRSA that infected DCI Huntley is traceable to Ifield, leads to AC-12 arresting DCI Huntley on suspicion of murder. During questioning, DCI Huntley admits to killing Ifield, revealing she did it in self-defence, as well as attempting to set her husband up for the murder and accusing lawyer Lakewell of perverting the course of justice.

Later in the final episode, viewers discover it was Lakewell who used a burner phone to tip off ACC Hilton, who then ordered the attack on DS Arnott. In another twist, it's revealed the same burner phone was also used by Reznikova's attacker.

In an attempt to clear her name, DCI Huntley proves ACC Hilton was involved from a private phone number he gave her, and although ACC Hilton asked DC Desford to take Lakewell, DS Arnott and DCI Huntley manage to stop him, following a shoot-out in the office. Surrounded by armed police, DC Desford hands DS Arnott his weapon and he's later cuffed by officers.

The following morning, ACC Hilton's dead body is found at the same location as Oliver Stevens-Floyd, who was the social worker attempting to blow the whistle on child exploitation at Sands View boys' home. DS Fleming informs Superintendent Hastings that his body was found to make it look like suicide, insinuating the same could be the case for ACC Hilton.

In the end scene, it's revealed the coroner declared ACC Hilton's death as suicide, whilst DCI Huntley is currently serving 10 years in prison for manslaughter. Both Nick and Farmer's changes were dropped, whilst the section-15 notice against Superintendent Hastings was rescinded, as well as the accusation that he is 'H'.

When did it air?

Series four of Line of Duty first started on 26th March 2017, running with weekly episodes until 30th April 2017.

What channel was it on?

Following the huge success of the first three series on BBC Two, bosses at the BBC decided to promote the show to prime slot on BBC One for the fourth series.

How many episodes?

Series four is made up of six episodes in total.

How many viewers?

Following a move to BBC One, series four averaged 8.24 million viewers, almost four million more than the third series.

Who was in the cast of the fourth season?

As they do in series one-three, Martin Compston, Vicky McClure and Adrian Dunbar lead the cast as DS Steve Arnott, DS Kate Fleming and Superintendent Ted Hastings respectively. Westworld and ER actor Thandie Newton joins the cast as DCI Roz Huntley, with appearances from the likes of Jason Watkins, Paul Higgins and Nigel Boyle.

Check out the cast list for series four of Line of Duty below:

Martin Compston as DS Steve Arnott

Vicky McClure as DS Kate Fleming

Adrian Dunbar as Superintendent Ted Hastings

Thandie Newton as DCI Roseanne “Roz” Huntley

Jason Watkins as Forensic Coordinator Tim Ifield

Paul Higgins as ACC Derek Hilton

Aiysha Hart as DS Sam Railston

Maya Sondhi as PC Maneet Bindra

Lee Ingleby as Nick Huntley

Patrick Baladi as Jimmy Lakewell

Gaite Jansen as Hana Reznikova

Claudia Jessie as DC Jodie Taylor

Patrick FitzSymons as DCI Mark Moffatt

Mark Stobbart as DS Neil Twyler

Scott Reid as Michael Farmer

Anneika Rose as PC Farida Jatri

Elva Trill as Gemma Riley

Royce Pierreson as DC Jamie Desford

Vineeta Rishi as FC Rupal Pandit

Nigel Boyle as DCI Ian Buckells

Harriet Cains as Jade Hopkirk

Tony Pitts as DCS Lester Hargreaves

How can I watch it?

You can watch Line of Duty for free on BBC iPlayer now. It's also available to watch on streaming service Netflix.

Who wrote it?

Former hospital doctor and Royal Air Force officer Jed Mercurio wrote the fourth series of Line of Duty, just as he did with the first three series.

You can see a full list of other TV shows Jed has worked on right here, including Bloodlands and Trigger Point.

Where was it filmed?

Filming for series four once again took place in Belfast, Northern Ireland. The old Belfast Metropolitan College on Tower Street was used DCI Roz Huntley’s Polk Avenue Police Station, whilst the Invest Northern Ireland building on Bedford Street was once again used as the exterior of AC-12's headquarters.

Production for the fourth series was between 29th August and 16th December 2016.

Check out the Line of Duty filming locations below:

Now read:

Line of Duty: Everything that happened in series one

Line of Duty: Everything that happened in series two

Line of Duty: Everything that happened in series three

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