24/04/2021 05:00 BST | Updated 24/04/2021 05:00 BST

Line Of Duty's Key Series 6 Theories: An Examination

With the hit BBC cop show hurtling towards its climax, we put some of the most popular fan theories under the spotlight.

With only two episodes of Line Of Duty left in the current series, we’re just a matter of days away from getting some serious answers about AC-12′s investigation into Operation Lighthouse. 

As things stand, one beloved officer’s life is hanging in the balance and there’s a massive connection to a previous series, while several names are also in the frame as the hunt for the “fourth man” gathers pace. 

As a result, there are many theories circulating among armchair detectives, who reckon they’ve cracked various parts of the case.


We’ve therefore taken it upon ourselves to round up some of the most popular theories doing the rounds on social media, so we can take a closer look at the evidence that supports them and try to work out how likely it is that they’re accurate... 

Theory 1: Fleming isn’t dead

Fleming had a tense, armed stand-off with Pilkington

DI Kate Fleming was feared dead at the end of the most recent episode, after a tense armed stand-off with corrupt officer Ryan Pilkington

Just before the credits rolled, two ominous gunshots rang out, leaving viewers wondering if writer Jed Mercurio had killed off the beloved officer. 

However, it looks like the answer to that question could actually be hidden in the official BBC trailer for series six, which debuted earlier this year. 


  • In a scene that is yet to air in the series, Davidson is seen wearing the same clothes in the same setting as the last episode, as she insists: “Kate, I had nothing to do with it”
  • Fleming is also seen standing opposite her in the clip
Davidson addresses Fleming in a scene from the trailer that is yet to air on TV
Fleming looks very much alive here
  • Another teaser released before the series showed Davidson holding her hands up in the air as Fleming stands next to her after Hastings and Arnott arrive on the scene


Likelihood: While Mercurio refused to rule out the possibility of one of the major characters dying in this series in a press conference earlier this year, this clip certainly seems to be proof Fleming survives. 

Adrian Dunbar – who plays Hastings – also hinted that fans’ suspicions about the trailer were correct.

During an appearance on Good Morning Britain, he said: “I know [what happens to Kate] and a lot of Line Of Duty fans know. A lot of Line Of Duty fans know what’s going on. All will be revealed in the fullness of time. There’s been a very big clue.”

Of course, it could still be a red herring that’s been deliberately placed in the trailer to make us think exactly this (we’d put nothing past those sneaky Line Of Duty bosses), but we’d say it’s a fair bet Fleming will live to fight another day. 

Theory 2: Carmichael is ‘H’

DCS Carmichael recently returned to Line Of Duty

AC-3’s DCS Patricia Carmichael has only just returned to the series, but she’s already come under the suspicion of fans. 

Some think she could be the artist formerly known as “H”, thanks to something Jimmy Lakewell said prior to being murdered by Lee Banks in prison. 

As one Twitter user wrote: “I think Carmichael is H. Jimmy Lakewell told Steve to look more into the race claim. Take away Raceclaim from Carmichael and what do you have left... H.”


  • She was appointed by Chief Constable Philip Osbourne – someone who we now know is heavily corrupt and has actively sought to scale back anti-corruption units
  • She withdrew the surveillance on Ryan Pilkington and DCI Jo Davidson, just as AC-12 were making progress on the case
  • She’s sought to have the charges against DSU Ian Buckells dropped
  • She was keen to nail Hastings as “H” in the last series – was she in on the plot to frame him?

Likelihood: While something like an anagram might not seem hugely significant, let’s not forget fans picked up on small clues like this in the last series alluded to Gill Biggeloe being in on the plot to frame Hastings

As much as we love Carmichael’s smugness, there’s definitely something suspicious about her arrival back at AC-12, especially as she has been spared from the axe by Osborne. Either she’s in on it with him, or she’s being manipulated by him to derail the investigation into Operation Lighthouse. 

Theory 3: Hastings is corrupt

Hastings is under the spotlight once again

Hastings’ conduct has been under the microscope since series four now, and while the last series saw him framed and subsequently cleared of being “H”, he could still be “the fourth man” – or a bent copper at the very least.  


  • He tipped off Lee Banks about a police rat being in the OCG
  • He pocketed £50,000 of the money Mark Moffatt tried to bribe him with, and gifted it to Steph Corbett
  • He didn’t pull Ryan Pilkington in when he posed a clear danger to Fleming’s life, instead choosing to keep him under surveillance 
  • A graffitied “H” appeared next to him in a scene with Fleming in the underpass

Likelihood: Of course, some of Hastings’ behaviour hasn’t been within “the letter of the law”, but we refuse to believe the much-loved AC-12 boss is in league with organised crime – mainly because there’s an explanation for some of his conduct.  

We’re guessing that Hastings tipped Banks off as revenge against Corbett for his brutal attack on his ex-wife in series five and has been paying Corbett’s widow money out of guilt – especially after it was revealed Hastings and Corbett had a shared history through the deceased UCO’s late mother, Anne-Marie McGillis. 

However, he’s still going to have a hard time explaining all of this if Arnott tells anyone about his recent discoveries about the gaffer.

Theory 4: Corbett was Hastings’ love child

Hastings with Corbett's widow Steph

The exact reason why Hastings is still in contact with Steph Corbett is yet to be revealed, with some fans speculating that he was actually John Corbett’s father.


  • His continued visits to and contact with Steph Corbett, which could suggest he is also spending time with his grandchildren
  • Hastings helped Steph out financially
  • Steph has being lying to Arnott about Hastings
  • The fact it’s still unclear if Hastings’ relationship with Anne-Marie McGillis crossed a line

Likelihood: A whole series on and we’re still convinced Hastings is Corbett’s father.

Obviously, Hastings would only have found out following Corbett’s death, when it was revealed Corbett had been emotionally manipulated by the OCG (via Gill Biggeloe) into going after Hastings. Corbett believed him to be responsible for the death of his mother when she acted as an informant during Hastings’ time in the Royal Ulster Constabulary. 

While Hastings denied ever getting too close to Anne-Marie (something we don’t believe), being responsible for his son’s death would certainly be an explanation for his guilt and continued contact with Steph – although we’re sure that Steph is still very much in the dark about Hastings’ little visit to Lee Banks. 

Theory 5: Thurwell is the ‘fourth man’

Marcus Thurwell will be played by James Nesbitt

Not much is currently known about former officer Marcus Thurwell, who was first mentioned back in series three, when we found out he was the ISO on the original investigation into the Sands View boys home.

His name has cropped up again in relation to the Lawrence Christopher case, with Arnott believing he has a high level of influence with the OCG.

Reports have claimed that we will meet the character – played by James Nesbitt – in upcoming episodes, suggesting he’s a significant figure. 


  • He was involved in the Lawrence Christopher case and the original investigation into Sands View boys home scandal – both have a connection to the now-deceased OCG boss Tommy Hunter
  • Would have benefited from journalist Gail Vella’s murder, as she’d already established links between the two cases
  • He is currently on the run, living in Spain

Likelihood: While we don’t doubt for a minute Thurwell is as corrupt as they come and in league with the OCG, it feels like Line Of Duty bosses wouldn’t unmask a character we haven’t previously met as “the fourth man” given the hunt for him (or her) has been so central to the last few series.

We feel it’s much more likely to be a character we know already, otherwise the reveal risks being a let down. We do suspect Thurwell will be instrumental in helping to uncover the “fourth man”, though. 

Theory 6: Osborne is the ‘fourth man’

Philip Osborne covered up what happened in the police killing of Karim Ali

Philip Osborne is the current Chief Constable of Central Police, and his rise to power has been a concern for AC-12, especially following recent things about him that have come to light in the Operation Lighthouse.

Could he be the “fourth man”?


  • Osborne covered up what happened in the police killing of Karim Ali back in series one, so we already know he’s corrupt
  • He has unveiled plans to scale back anti-corruption units at a time when AC-12 are making strides in their investigation
  • PCC Sindwhani says he has been “thrown under the bus” by Osborne, encouraging Hastings to continue to go after him
  • Worked on the Lawrence Christopher case, so therefore would have benefitted from Gail Vella’s murder
  • He’s at the very top of the force so is able to wield huge power

Likelihood: Osborne hadn’t been seen on screen since series one, and has so far only appeared in newly-recorded flashbacks in series six, where he is depicted in Gail Vella’s news reports. There’s definitely significance as to why he is suddenly back in the story, especially as he has been promoted to the highest rank in Central Police and is cutting back AC-12 operations. 

But similarly to Thurwell, we feel it would be more of a big reveal to unmask a character who has made more appearances in the show, like PCC Sindwhani or DCC Wise. 

While Sindwhani has said he is leaving the force over Osborne and told Hastings he’s actually on his side, there could still be a lot more to his story. We also haven’t forgotten the footage of him walking out on an interview with Vella when she pressed about the Sands View boys home scandal.

Theory 7: Chloe Bishop is Tony Gates’ daughter

Chloe Bishop and Tony Gates

DC Chloe Bishop has proved herself to be a valuable asset to AC-12 since her arrival on the scene at the start of the series. At present, we know little about her character outside of work, but some have spotted she shares the same first name as the daughter of series one antagonist DCI Tony Gates. 


  • There’s not actually much to suggest this other than the two characters are both named Chloe

Likelihood: Chloe Gates was a young child when she made her first appearance in Line Of Duty 10 years ago, looking around the age of a late-primary, early-secondary school child. 

While we don’t know how old Chloe Bishop is, Shalom Brune-Franklin, who plays her, is 26. Therefore, working off the assumption her character is a similar age, Chloe Bishop would be too old to be Gates’ daughter. 

Chloe Bishop is likely too old to be Chloe Gates, who appeared on the show as a child

We also don’t quite see how it would be relevant to the story to have DC Bishop be Gates’ daughter, or for her to have hidden this from her colleagues. 

As far as his family are aware, Gates died in the line of duty, and he while did work with the OCG, he only did so because he was being blackmailed.

Therefore, it would be highly unlikely the OCG had hired his daughter to continue his work from inside the police force.

Line Of Duty continues on Sunday at 9pm on BBC One.