WARNING. This article contains spoilers of the highest order.  

The hunt for “H” is finally over. 

Yes, after a four-year wait, we now know that DSU Ian Buckells was Line Of Duty’s mystery baddie all along. 

The bent copper, who had been helping to lead a clandestine network of corrupt police officers in league with organised crime, was unmasked during Sunday night’s blockbuster series finale.

Many other long-running storylines also wrapped up during the episode, as Gail Vella’s killer was confirmed and Superintendent Ted Hastings revealed the true story behind Lee Banks, John Corbett and the £50k sum of money.

If your head is still spinning trying to take all the information in, here’s a full recap…

The first big development of the episode saw DI Steve Arnott finally attend a medical appointment where he revealed the truth about his reliance on painkillers, and was asked to surrender his firearms licence, before telling Hastings about what had been going on.  

After this came the revelation that a lockbox had been found beneath the OCG’s gun workshop floor.

Inside it was the workshopped pistol used to kill Gail Vella, as well as clothes and gloves belonging to the shooter, which DNA testing proved was Carl Banks.

Also in the box were the knives that killed PC Maneet Bindra and undercover officer John Corbett, both of which had Ryan Pilkington’s prints on. 

The knife the OCG used to kill Jackie Laverty in series one was also recovered, with DCI Tony Gates’ prints on it – although we already knew the OCG planted his prints on the weapon so they could use it as leverage to coerce him into working with them. 

While questioning if there was any evidence that related to Marcus Thurwell or Ian Buckells, Arnott also mentioned Chief Constable Philip Osborne’s name, much to the shock of DS Chris Lomax…

Back at AC-12, it was discovered that Marcus Thurwell was indeed dead – despite the fan theories – as the bodies of him and his wife were formally identified, having been strangled to death at their Spanish villa a number of weeks earlier. 

At the property, police found devices that had made contact with DCI Jo Davidson and OCG member Lisa McQueen. However, it turned out that the communication actually originated in the UK and was routed via Spain so that the IP would be a decoy, and Thurwell used as a stooge.

Specialist Technician Amanda Yao then arrived with news of a recent message that had just been intercepted, with the sender saying Jo Davidson was “definately” high risk. 

The misspelling spiked AC-12’s suspicions as it matched the way “the fourth man” had spelled “definitely” when in contact with Lisa McQueen in series five. As a result, DC Chloe Bishop was asked to go through all the Operation Lighthouse and Lawrence Christopher files to see if there were any reports filed by officers that contained the same misspelling. 

As Hastings, Fleming and Arnott rushed to Blackthorn Prison to try and get Davidson to safety, they discovered a production order had been issued calling for Davidson to attend an interview at Hillside Lane station, which had supposedly been co-signed by DS Chris Lomax and DI Fleming. 

Realising it had been forged, they rushed to find the convoy Davidson had been taken on with corrupt prison officers. 

After managing to intercept it, Arnott and Fleming planted themselves in the van, and continued with the route, where they were ambushed by OCG who were ready to kill Davidson. However, the balaclava-clad men were quickly apprehended and the corrupt prison officers arrested.  

With Davidson having been taken to safety, she was interviewed by Fleming and Arnott who offered her witness protection if she were to give up the “fourth man”. 

Davidson then said former OCG boss Tommy Hunter (who was both her uncle and her father) had told her that her father was a bent police officer, who she was made to fear and take orders from. This man was revealed to be former officer and known peadophile Patrick Fairbank, who is serving time for his involvement in the Sands View Boys Home scandal. 

However, after a search of his prison cell found nothing, it became clear that Hunter had manipulated Davidson into thinking Fairbank was also the fourth man as well as her father, which he was not. 

Back at AC-12, Bishop’s review of misspellings the Vella and Christopher files has revealed their real identity, much to the shock of Hastings, Fleming and Arnott. 

As Hastings went to tell DCS Patricia Carmichael of their breakthrough, Fleming and Arnott warned him against widely publicising their findings, as their own professional conduct would come under scrutiny. 

It was at this point the pair revealed they knew about Hastings blowing Corbett’s cover and subsequently paying his widow money. 

Confessing his involvement in the events leading up to Corbett’s death, Hastings maintained that he did not disclose Corbett’s identity to Lee Banks during his visit to Blackthorn Prison in series five, instead telling him that there “was an informant in the OCG” and “no more than that”. This was consistent with Banks’ account that he gave to Arnott. 

Hastings claimed he wanted to send a warning to Corbett, so that when he found out the OCG knew about a rat he would go to ground. Admitting he knew there was risk to Corbett’s life, Hastings added that he believed Corbett “had to coming to him in spades” as he’d been involved in the death of four officers – including PC Bindra – and had also violently attacked his wife. 

Hastings said that what he didn’t know at this point was that he was the son of woman he “cared deeply about many years ago” – this woman being Anne Marie McGillis, a CHIS who Hastings got close to when he worked in the Royal Ulster Constabulary. He called his actions “his biggest regret”.

As for the money, Hastings said he was originally tricked into accepting it (by corrupt former officer Mark Moffatt who was part of the conspiracy to set Hastings up as “H” with Gill Biggeloe in series five), and was blocked from returning it, but it was found before he could hand it in as evidence. 

He explained he split the £100k into two halves as he realised it was a bribe that could turn nasty, intending to use it as insurance against the OCG if they came looking.

With one half of the £50k never found, he then gifted this to Steph Corbett following John’s death by way of atonement, although she remains in the dark about the real version of events that led to her husband’s death. 

During this conversation, Hastings also revealed Steph had told him about Arnott’s painkiller addiction and that he’d seen to it that Arnott didn’t face disciplinary action.

Finally, in what was possibly the longest, most tense reveal in Line Of Duty, the fourth man was finally unmasked. 

After walking through AC-12 HQ and sitting down at the desk, the camera panned up to reveal DSU Ian Buckells sitting opposite Hastings, Fleming and Arnott. 

He faced intense questioning about his double life, but various pieces of evidence were produced to confirm he was the final officer leading the clandestine network of corrupt officers in collusion with organised crime. 

Buckells had proved to be grossly incompetent at his job over the years, but it was this that meant his corruption was never spotted – in fact, he was so convincing that Davidson was even trying to frame him, whilst not realising he was the one actually in charge. 

“Yeah right, I’m a blundering fool? I’m the one who’s made total mugs out of you lot,” he told AC-12. 

Buckells then tried to go for immunity by agreeing to co-operate, quoting Osborne and saying that “institutionalised corruption doesn’t officially exist” in Central Police and therefore AC-12 wouldn’t be able to make the charges stick. 

He revealed that prior to his death, Hunter was always the top man of the OCG, but it then split into disparate groups, with Thurwell and Fairbank initially overseeing control of the network of bent officers, before DI Matthew “Dot” Cottan and ACC Derek Hilton became the top dogs.

After their deaths, Buckells was the only one left still serving in the police. 

He claimed to just take orders from the OCGs, and they kept asking him to sort bigger and bigger affairs, like the Eastfield depot raid in series five. 

AC-12 put it to him that the OCG didn’t actually order Vella’s murder as they had no real reason to. The only connection they had to her on their side was through Hunter – who is long dead – and his son Darren (who was one of the gang who attacked Lawrence Christopher), who Fleming noted was a “nobody” to the OCG. 

However, two police officers now involved in the original Christopher investigation were now high-ranking – Buckells and Osborne – meaning they had the most motive to want her dead, as she was beginning to establish links that proved institutionalised corruption in the force.  

Buckells was then asked if he colluded with Osborne to have Vella killed, and while he didn’t reply, he was screwed either way – if he declined to help with the investigation, he would be ineligible for witness protection, and by confessing conspiracy to murder, he would then be ineligible for immunity from prosecution. 

Having wrapped by far their biggest case ever, Fleming and Arnott headed to the pub to celebrate, where Fleming revealed she would accept Hastings’ offer of a job back with AC-12 should he remain as the gaffer. 

Arnott opened up to his “mate” about his painkiller addiction and revealed he wanted to keep seeing Steph Corbett romantically, but felt torn.

Fleming was then seen visiting the department’s medical officer for an unspecified reason. 

Back at AC-12, Arnott and Fleming revealed to DCS Patricia Carmichael that they were now intending to go after Darren Hunter for his part in Lawrence Christopher’s death in order to get a conviction.

Arnott suggested launching an investigation into whether other members of Marcus Thurwell’s team might have been involved in the cover-up of the Lawrence Christopher case, given many of them are still serving officers. Carmichael informed him that such cases “aren’t a priority”. 

Like Osborne, she refused to entertain the idea there is a problem of institutionalised corruption in the force – something the Chief Constable reiterated in a press conference about finding Gail Vella’s killer, much to Hastings’ disgust. 

Hastings revealed he would be appealing the decision to push him into early retirement, but as he went to leave the building, he returned to Carmichael’s office and confessed his role in Corbett’s death. 

“What do you expect me to do with that information?” she asked. 

“That’s entirely up to you, ma’am,” he replied. “But whatever you do, you do because you care about truth and accountability. You do it because you carry the fire.”

A pre-credits sequence then revealed all proceedings against Terry Boyle in Gail Vella’s murder had been dropped and he had been rehoused, while Jo Davidson was granted witness protection and was living with a new parter in an undisclosed location. Darren Hunter was also discovered to be under investigation for Christopher’s murder, while PS Farida Jatri was freed from prison and returned to the police force.  

Plans to slimline anti-corruption were also ploughing ahead, with DCS Carmichael remaining in charge of AC-12.

“Close colleagues” of the Chief Constable had been appointed to other senior positions in anti-corruption, with AC-12’s powers to curb wrongdoing in public office never weaker, which suggests he is suppressing information.

Meanwhile, Central Police submitted an application for public-interest immunity in legal proceedings against Buckells, which means that if it is successful, no evidence about institutionalised corruption would be heard in court. 

This suggests they don’t want him to face justice as it could expose something much larger…

With the photos of Jo Davidson, John Corbett, Roz Huntley, Danny Waldron, Lindsay Denton and Tony Gates packed up into a box at the end of the episode, things looked pretty final for AC-12, leading to questions about whether there will be another series of Line Of Duty.

However, there were a lot of loose ends – specifically around Carmichael, Osborne and even Lomax – and the suggestion that there’s a lot more to the Lawrence Christopher case yet to be discovered. 

All six series of Line Of Duty are available to stream on BBC iPlayer.