Vicky McClure and Jo Davidson as Kate Fleming and Jo Davidson in Line of Duty on BBC One

Line Of Duty season 6: 24 brilliant fan theories that could explain everything

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Don’t even think about calling yourself a Line Of Duty fan until you’ve read through these compelling fan theories… 

Updated on 2 May: There is just one more episode of Line Of Duty season six left, and yet we have more questions than ever.

As such, the notes in our trusty notepads are getting a little… well, a little muddled. Is Kate Fleming (Vicky McClure) really the villain so many fans believe her to be? Is Jo Davidson (Kelly Macdonald) destined to be killed at the hands of a corrupt police officer? Is Steve Arnott (Martin Compston) destined for a desperately unhappy ending? And what is the deal with Ian Buckells (Nigel Boyle)?

Also, is the increasingly desperate Ted Hastings (Adrian Dunbar) as noble as he appears? Is Chloe Bishop (Shalom Brune-Franklin) a dream come true, or a nightmare in disguise? What is DCS Patricia Carmichael (Anna Maxwell Martin)’s problem? And is Marcus Thurwell (James Nesbitt) the man that Jo always believed to be her dad?

The most important question every single fan of the BBC crime series is desperate to have answered, though, is this; who the hell is H?

To help us all streamline our notes a little, we’ve looked out some of the most compelling Line Of Duty fan theories. Which means that, yes, there are spoilers ahead, so be sure you’re up-to-date with the TV drama before reading.

And fair warning: you’ll never look at the show the same way again after reading these…

Is Buckells really the buffoon we all think he is?

Basically nobody expects much from Buckells, but he’s been linked to this case from the get-go… and now some savvy viewers have pointed out a big H-shaped hint in his office.

Yup. we’re talking about his framed picture of a person playing golf, hung on the wall in Buckells’s office. 

Hmm. Could this be a reference to “The Caddy”, and the OCG leadership’s known fondness for the sport? Or is it just… is Buckells just the sort of guy who enjoys a round of golf?

Only time will tell, we guess.

Is there a secret link between Marcus Thurwell and Steph Corbett?

As reported on 30 April: Oh we know, trust us. We know he’s supposed to be dead. But some viewers have taken to Twitter to speculate that Steph Corbett (Amy De Bhrún) could be hiding the real Marcus Thurwell in her home.

“I predict that Marcus Thurwell is living with Steph Corbett,” tweeted one viewer knowingly.

“The bodies in Spain were from the freezer.”

Another added: “Marcus Thurwell is staying with Steph Corbett and the money in the attic is his.”

And still one more theorised: “Marcus Thurwell is alive and living in the UK with Steph Corbett (why does she always go outside to make phone calls?!).”

Will Ted Hastings die in the season finale?

As reported on 28 April: A horrifying thought? Absolutely, but that hasn’t stopped fans going there after our beloved Hastings (“the epitome of an old battle”) is hiding a terminal diagnosis from his fellow AC-12 team members.

Why? Well, not just because he’s spent more than a few moments this season looking anguished in a stairwell (although that has only served to cement the idea). Rather, it’s because he uttered this fateful line to Steve during Sunday’s penultimate episode.

“Sometimes you don’t lose, son. You just run out of time.”

Throw in Ted’s sick leave at the end of series five, and you have a recipe for an out-of-control fan theory, quite frankly.

Why did Carmichael tap out ‘H’ in Morse code?

Eagle-eyed viewers noticed Carmichael tapping her pen four times during Sunday night’s record-breaking interview scene, and have thus theorised that she is “H”. Why? Because the tapping sound spells out “H” in Morse code, which we all learned from Dot Cottan (Craig Parkinson) as he died.

Of course, Anna Maxwell Martin, who plays Carmichael, has dismissed the theories. Indeed, during a recent This Morning interview, she explained: “I think I was just [tapping because I was] bored, because those scenes are very long. 

“I think I was just like, ‘what am I saying next?’”

Is she just trying to throw us off the track, though? Your guess is as good as ours.

Is Marcus Thurwell really Jo’s other dad?

As reported on 25 April: Look, we know what the forensic report says; Tommy Hunter is both Jo’s father and uncle (yikes). But Jo always believed that her dad was a police officer – and it’s clear that LOD bosses hired James Nesbitt for a meatier role than a non-speaking mugshot role.

Plus, whenever Hastings pressed Jo as to whether she knows Thurwell, she responded with a very meaningful “no comment.” Which surely means… yes, right?

And has he faked his own death?

Oh sure, we know what everyone was told at the end of the episode; two bodies were found at Thurwell’s last known address. The implication? That it’s the bent copper and his wife, and someone’s done them in.

But… well, as several people on Twitter have noted already, the masked police officer delivering this information looked AWFULLY familiar.


Is Carmichael really the H we’ve all been looking for?

Look, she’s been tracking AC-12, she basically refused to let Jo speak in the interrogation, she had Chief Constable Philip Osborne’s image removed from the investigation board, and two female police officers advanced on Jo in a very menacing manner at the episode’s end.

Throw in that handy anagram theory from last week, and you have a recipe for one serious bent copper.

As one viewer tweeted: “We all know Patricia Carmichael is H. Jimmy Lakewell said ‘look beyond the RACE CLAIM to find H’.”

“So take the letters of RACE CLAIM from the letters of CARMICHAEL. What do you get? H. Solved it.” 

H didn’t want Kate dead; instead, they set Ryan up to die

As reported on 22 April: This one comes courtesy of Reddit, and it goes a little something like this: “The intention was not for Kate to be killed, but for Ryan to be killed.”

The theorist goes on to explain that H asked Jo to get rid of Kate, knowing she wouldn’t be able to do it and that she’d ask Ryan to fire the fatal shot instead.

“H knows Kate is firearms trained and colluding with AC12, so possibly armed/being protected,” they add. “So I believe that H intended for Ryan to be killed by Kate, Jo or AC-12 in a shootout because he is a liability [and] knows far too much.

“Without Ryan, AC12 are missing a vital link.”

Gregory Piper as Ryan Pilkington in Line Of Duty
Did H set Ryan Pilkington up to die?

Hmm, we like it. We like it. However, it does add some extra credence to the theory that Kate is actually H; after all, she was all too aware of Ryan’s bad behaviour, and she was armed when she went into her confrontation with him.

Curiouser and curiouser, eh?

Is DS Chris Lomax the ultimate bent copper?

As reported on 21 April: Look, we’ve always liked Lomax; he seems like a straight-up guy, and he’s always seemingly had Kate’s back. But in episode five, Chloe Bishop began busily investigating the death of Lawrence Christopher, a Black man who was killed in police custody in 2003 – and eagle-eyed fans spotted a very familiar face amid the gang members involved in his death.

Check it out:

We’ve said it before and we’ll say it again: mother of god.

Now, it could be that Lomax is the bent copper who’s been under our noses this entire time. It could be that his mugshot, plus his friendship with Kate, gives extra credence to the idea that our beloved DI Fleming is actually ‘H’ herself. Or it could be evidence that Lomax was working undercover on the case for AC-12 – and is, therefore, working undercover for them right now at The Hill (either helping assist Kate in her investigations, or doing a little digging into her background).

Only time will tell, we guess…

Where are Mark and Josh Fleming?

In earlier episodes, it was made abundantly clear that Kate has split – or at least temporarily separated – from her husband Mark, with whom she has a young son, Josh. But why?

Some viewers have leapt to conclusions, insisting that the relationship was irreparably damaged by Kate putting in long hours at work. Others have suggested, though, that this minute detail will be used to explain her role as ‘H’ in later episodes. Hmm.

Is Jo Davidson a product of incest?

As reported on 19 April: It was confirmed in episode five that Jo Davidson is likely a blood relative of Tommy Hunter (Brian McCardie) – but the forensic report also noted “runs of homozygosity” in her DNA.

So what does this mean? Well, the term ‘homozygosity’ is used to describe the possession of two identical alleles of a particular gene or genes by an individual. Which, in lay(wo)man’s terms, means that she’s a product of incest. 

That’s right; she inherited the same DNA sequence for a gene from both her biological father and biological mother, indicating that they were related. So, who was Jo’s mother? Answers on a postcard, please.

Did Marcus Thurwell give the order to kill Gail Vella?

It’s made pretty clear in this episode that Ian Buckells (Nigel Boyle), Philip Osborne (Oweb Teale), or Marcus Thurwell (James Nesbitt) who gave the order to kill Gail Vella (Andi Osho). And most people’s, at this point, is on the latter. 

Why? Well, because she was about to expose all of Thurwell’s wicked misdeeds on a podcast. And because she was murdered just one day before she was due to interview Patrick Fairbank (George Costigan) – aka the senior officer in prison for child sex offences at Sands View – about Thurwell, too.

Line Of Duty episode 6 season six recap
Anna Maxwell Martin recently starred as Chief Superintendent Patricia Carmichael in Line Of Duty.

Has Kate really been killed off?

Episode five ended with Kate and Ryan pointing their guns at one another, tensions bubbling to a ridiculous new height, and a fade-to-black as two gunshots rang out.

So, is Kate dead? Hardly.

Viewers have once again turned detective, flooding Twitter with screenshots from an old trailer – screenshots from an old trailer, mind, which appears to show Jo and Kate a) wearing the same clothes they were in last night’s episode, b) alive and well, and c) together in a scene that we don’t think has been shown yet.

“Screen grab from #Lineofduty session 6 @BBC trailer,” wrote one. "#katefleming looks pissed, #jodavidson has her hands in the air. THIS SCENE HASN’T OCCURRED YET. #katefleming lives for at least 1 more episode. #motherofgod.”

Is Line Of Duty season 6 inspired by this chilling true story?

As reported on 12 April: Many people have taken to Twitter to suggest that the murder of Gail Vella (Andi Osho) is based on a true crime story: the murder of Daphne Caruana Galizia.

The Maltese anti-corruption journalist, whose maiden name was Vella, made a name for herself exposing cronyism and sleaze within Malta’s elite. On 16 October 2017, though, Caruana Galizia died close to her home when a car bomb was detonated inside her vehicle,

Vincent Muscat was found guilty of murder in February and sentenced to 15 years after being convicted.

“@jed_mercurio been wondering, is #LOD6 somewhat inspired from the unresolved murder case of #DaphneCaruanaGalizia?” tweeted one viewer, after spotting the link.

“My first hunch was the use of the Maltese surname #Vella. Also, same car model, similar journalism and similar potential motive!”

Mercurio has seemingly confirmed the theory, tweeting back: “The Gaffer has been complaining that none of the detectives out there had spotted this clue.

“He’ll probably ask you to join AC-12.”

Is Jo related to Tommy Hunter?

Line Of Duty’s original ‘Big Bad’, Tommy Hunter (Brian McCardie) wasn’t just the former leader of season one’s OCG; he was also a paedophile who abused young boys in Sands View children’s home.

Many have begun to suspect that Jo is Tommy’s daughter – which would explain why she adamantly told Farida that she has “no family.” However, it’s worth remembering that Tommy was born in 1965 and Jo was born in 1979, which would mean he became a father at the tender age of 14.

Not impossible, but… yeah. Maybe they’re siblings?

Is Jo the sister of… Kate Fleming?

It would certainly add a horrible new spin to the blossoming relationship between the pair, but countless LOD viewers have taken to Twitter to suggest that Jo and Kate are sisters. Mainly, because Kate was the only member of AC-12 who wasn’t present when the DNA results were shared.

“I’m going to go with Jo Davidson either being Jackie Laverty’s given-up-at-birth daughter or… and bear with me… Kate Fleming’s sister that Kate doesn’t know about,” tweeted one.


Is Jo the daughter of Ted Hastings?

Now, we all know that Ted (Adrian Dunbar) had a short-lived relationship with Anne-Marie McGillis, a police informant in Northern Ireland – and a lot of people have pointed out that a photograph in Jo’s flat bears an uncanny resemblance to Anne-Marie, too.

Could Jo be the daughter Ted never knew he had?

Gail Vella exposed a connection between the foster care system, the OCG, and the police

This one is pretty intense, so we’ll let Twitter user Eleanor Crossland explain it:

Now, we all know that Ted (Adrian Dunbar) had a short-lived relationship with Anne-Marie McGillis, a police informant in Northern Ireland – and a lot of people have pointed out that a photograph in Jo’s flat bears an uncanny resemblance to Anne-Marie, too.

Could Jo be the daughter Ted never knew he had?

H isn’t a person – it’s The Hill

This gem comes courtesy of avid LOD viewer Allan Ramsay, who tweeted: “The fourth ‘H’ isn’t a person, it’s a place: The Hill. A station where the OCG holds enough sway to constantly rotate bent coppers through the ranks.”

Check it out:

This theory is made all the more compelling by one of the comments beneath it, which reads: “Genius! It would also correlate to Dot’s death blinking… H [was the] first letter, [so the] second would be a vowel and he made it past G, so the second letter isn’t A or E, which exonerates Hastings.

“If he made it to I, then he could have been hinting at Hilton, who recruited him… or The Hill.”

Others, meanwhile, have tweeted a variation on this theory, noting: “H is Headquarters!”

We’re so into this.

Jo Davidson is John Corbett’s sister

As reported on 8 April: The first episode of season six saw Jo Davidson return to her apartment – her apartment which, this writer hastens to add, was locked up tighter than an escape room. 

Detective Chief Inspector Joanne Davidson
Kelly Macdonald stars in Line Of Duty season six as Detective Chief Inspector Joanne Davidson.

She then spent a moment looking at an old picture of her mum, before throwing a glass at it in rage. And, in that split second, several eagle-eyed viewers noted that Davidson’s mother looked an awful lot like Anne-Marie McGillis, aka the former police informant and mother to the late John Corbett (Stephen Graham). 

Could it be that Jo has infiltrated the police in order to seek vengeance for her dead brother?

Steph Corbett is H (or, at least, working with H)

While we’re on the subject of the Corbett family, it’s worth noting that Ted Hastings (Adrian Dunbar) used Anne-Marie as an informant back in the day.

This was a decision which a) led to John’s throat being slit in season five, and b) resulted in Ted feeling so responsible for the bent copper’s death that he gave his widow, Steph (Amy De Bhrún), a whopping £50k.

Now, many have questioned why a relatively minor character like Steph Corbett has been brought back for season six. And many have pointed out that there’s a suspicious pattern of Hs all over her kitchen, too.

Could Jed Mercurio be messing with us? Or is Steph going to give both Ted and Steve Arnott (Martin Compston) a nasty surprise before the season is out?

Chloe Bishop is Tony Gates’ daughter

Back in the very first season of Line Of Duty, Steve found himself going head-to-head with DCI Tony Gates (Lennie James). As in, yes, the bent copper who had an affair with the late Jackie Laverty (Gina McKee) and ended up doing work for an OCG as a result of his infidelity.

Tony died by suicide at the end of the first series, leaving behind a wife, Jools, and two daughters, Natalie… and Chloe.

Chloe Bishop in Line Of Duty
Many have begun to suspect Chloe Bishop in Line Of Duty.

“Holy Mother of God!” tweeted one viewer. “Has Chloe Bishop (Shalom Brune-Franklin) been ‘inserted’ into AC12 by a higher authority (’H’) to get revenge for what AC12 did to her father, DCI Tony Gates?”

Now, this could be a total red herring, but viewers have taken to Twitter to point out that Chloe Gates was last seen on screen nine years ago – which would make her roughly the same age as DC Chloe Bishop now.

Has Chloe changed her surname to protect her identity when working with the police? And, if so, is she working with AC-12 for powers of good or evil?

Kate Fleming is H

Wait, what?

Well, there have been a fair few hints that the final H is a woman – and plenty have pointed the finger at Kate Fleming, insisting she only began helping AC-12 after her former teammates learned that someone was corrupting murder investigations at The Hill. Covering her tracks, maybe?

As one viewer noted: “Kate is registered as Katherine in the system. Katherine has H in it. She’s the last one. I’m convinced.”

Then again, it seems just as likely that Kate was placed in The Hill by Ted so that she could work for AC-12 undercover.

“Do you think Hastings has put Kate undercover to investigate Buckells?” suggested one viewer. “But the side twist of Jo and the young PC???”

DS Ian Buckells is an undercover agent

We recently saw DS Ian Buckells arrested for his actions surrounding the investigation into the murder of Gail Vella… but fans have an intriguing theory about his role in it all.

As one person wrote: “I have a #LineOfDuty theory… Buckells is an undercover AC-12 agent known only to Hastings. Recruited through Masonic connection and instructed to get close to Ryan to find H.”

And one more added: “Buckells is an undercover AC-12 agent looking into Kate as being one of the Hs.”


Gail Vella is still alive

As Craig Parkinson, who portrayed Matthew ‘Dot’ Cottan in the show, said on BBC Sounds podcast Obsessed With Line of Duty: “Somebody is in that flat and there’s some connection with Gail Vella, the investigative journalist.

“You don’t cast someone like Andi Osho and then just have her as little magazine prints and stick them up on a kitchen wall.”

And the mysterious male voice on Gail’s podcast is…

Earlier this season, Steve reviewed a corrupt audio file which had been recovered from the laptop of Gail Vella.

“[Jimmy] Savile lied to cover them up,” Vella can be heard saying. “Some police officers not only accepted those lies, they propagated them. We’re losing our power to challenge lies.”

A mysterious male voice then responds: “There’s some people you can’t challenge.”

Viewers have since flocked to Twitter to share their theory that the voice belongs to none other than Jimmy Lakewell (Patrick Baladi).

For those who need a refresher, Lakewell was the corrupt lawyer of season four, who helped to cover up Operation Trapdoor and had strong links to DCI Roz Huntley (Thandie Newton).

More relevant than all of this, though? It was Lakewell who told the balaclava men where to find Steve, leading to the AC-12 copper being thrown down a flight of stairs and seriously injured. An injury which, as we’ve all seen this season, has led to him developing an addiction to painkillers.

Intriguing stuff… anyone else’s notebooks now overflowing with ideas?

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Line Of Duty season 6 airs weekly on BBC One, Sunday nights at 9pm.

Images: BBC

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Kayleigh Dray

Kayleigh Dray is Stylist’s digital editor-at-large. Her specialist topics include comic books, films, TV and feminism. On a weekend, you can usually find her drinking copious amounts of tea and playing boardgames with her friends.

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