Who is the final ‘H’ in Line of Duty? All the suspects, clues and theories

From Jo Davidson to Marcus Thurwell, from Patricia Carmichael to Philip Osborne – here are all the Line of Duty characters who could be that final "Fourth Man" in Central Police.

The H suspect pinboard in Line of Duty

We first started talking about “H” after Dot Cottan’s dying declaration in Line of Duty season three; when Kate started spelling out the alphabet, that initial was all he managed to give Kate before the medical team moved in. At first, it was assumed this was the first letter of a surname (like Hastings, Hargreaves, Hilton or Huntley).


But then John Corbett’s old covert operations manager suggested it was actually codename – and in season five, a re-examination of Dot’s dying declaration seemed to bear this out. By using his left hand to tap out “dot dot dot dot” (‘H’) in Morse Code, Dot was apparently trying to tell Kate that there were four “Dots” – i.e. four “Caddies”. We now know that three of these were Dot Cottan, Gill Biggeloe, and Derek Hilton. But who else?

We’ve pinned a big ‘H’ at the top of a virtual blue board – and put together our own collection of suspects from the Line of Duty cast.

Is Jo Davidson H?

Kelly Macdonald as Jo Davidson in Line of Duty (BBC)

At this point, we know for sure that Acting DSU (formerly DCI) Jo Davidson is bent. But could she also be H? Maybe!

Firstly, let’s talk about her background. As AC-12 has now worked out, Jo is related to Line of Duty’s original “big bad”, crime boss Tommy Hunter, who once led the OCG. More specifically, she is both his niece and daughter (!), as DNA analysis of “runs of homozygosity” has established.

So if Jo is from a family of (incestuous) criminals, it’s possible she was groomed from a young age to enter the police force at the age of 19 and act as the OCG’s “inside woman”. We’ve seen that modus operandi before, with both DI Matthew “Dot” Cottan (Craig Parkinson) and PC Ryan Pilkington (Gregory Piper) working from the inside.

Jo is pretty senior in the police force, and she’s been doing some seriously dodgy stuff. As soon as she became SIO on Operation Lighthouse, she did everything possible to frustrate the Gail Vella case – while somehow still looking like she was doing her best to catch the killer. She (presumably) made a call to the OCG when a tip-off came in about “Ross Turner” (Carl Banks), and then planted the phone in Farida’s house. She diverted the police convoy. She framed DI Ian Buckells. She led Ryan to a meeting with DI Kate Fleming (Vicky McClure) so he could execute her. It all adds up to something quite sinister.

However, we do have to wonder if Jo is the one doing the pushing, or if she is being pushed around. Can she be the all-powerful “H”, if the OCG is actually calling the shots and sending her orders via instant message? And if all her actions seem reactive, and designed to save her own skin? And when she seems too reluctant to work with the OCG any more?

Is Philip Osborne H?

Owen Teale plays Philip Osborne in Line of Duty

Chief Constable Philip Osborne has been a shadowy figure in the background of Line of Duty, appearing in season one – and now reemerging in season six as a central character, even though he’s yet to appear ‘in the flesh’ (it’s all been archive material and news footage).

“A bare-faced liar promoted to our highest office,” is how Hastings describes him. And if he’s in Central Police’s highest office, surely that makes him a prime candidate to be pulling all the strings? He could be the one who put bent cop Jo Davidson on the Gail Vella case to do his bidding.

We’re also told that Osborne is the mastermind behind this new move (communicated via Sindwhani and Wise) to merge AC-3, AC-9, and AC-12 while cutting the combined anti-corruption unit’s staff by 90 percent. He’s the one who’s been trying to force through Ted Hastings’ retirement.

Hastings was given a month until his retirement. But then Osborne jumped the gun and decided to bring AC-12 to their knees even sooner – appointing AC-3 boss Patricia Carmichael to take charge, and pulling funding for all surveillance operations. That put Kate Fleming and Terry Boyle in immediate danger, and freed Jo Davidson and Ryan Pilkington up to do whatever they liked.

Line of Duty fans have known since season one that Osborne is a villain: when his men killed an innocent man in a botched anti-terror operation by going to the wrong flat, he orchestrated a cover-up and cast DS Steve Arnott (Martin Compston) out of the fold when he refused to go along with it.

But season six suggests he’s not just villainous, but potentially corrupt – and working with the OCG. Back in 2003, he was one of the police officers working on the Lawrence Christopher case, in which (as AC-12 now realises) the police did everything they could to stop the killers being brought to justice; one of those killers was Tommy Hunter’s son, Darren.

Journalist Gail Vella (Andi Osho) started digging into that case, but as soon as it looked like she might be getting close to the truth about the cover-up, she ended up dead.

With a motive like that, and a job at the top of the police food-chain, Philip Osborne is a top candidate to be “H”.

Is Marcus Thurwell H?

James Nesbitt plays Marcus Thurwell in Line of Duty

We don’t know much about Marcus Thurwell (James Nesbitt) yet, but we do know he was SIO on the Lawrence Christopher case (and cover-up), and was also involved in the Sands View Boys’ Home case. The only reason he wasn’t brought in for questioning by AC-12 back then was that he’d already retired to Spain. Plus, Fairbank was arrested and convicted, so that was that.

Before season six, Thurwell had only been mentioned in passing. But now he has a face, and that face belongs to James Nesbitt, who is a reasonably famous actor – and therefore quite likely to be playing an important character.

So could “H” be a retired senior police officer calling the shots from Spain? It’s possible. In season five, police cyber expert Amanda Yao (Rosa Escoda) did mention something interesting when she tried to track down when the encrypted instant messages arriving on the OCG’s laptop were coming from: attempts to trace the messages sent to the device revealed “another user with internet protocol [IP] address located in Spain.”

However, as she added, “The user could have concealed their true location, connecting by multiple VPNs. They may be in Spain, they may be next door – there’s no way of knowing.”

But – maybe the user is in Spain! Maybe it’s Thurwell! You never know. But that would be quite an underwhelming outcome to a long-running storyline.

Is Ted Hastings H?

Adrian Dunbar plays Superintendent Ted Hastings in Line of Duty

AC-12’s beloved crusader against police corruption, Superintendent Ted Hastings, had a shocker in season five – and at one point, it even looked like he’d be going to jail as Carmichael built a solid case against him. Ultimately, his “best team” came to his rescue and presented new evidence, clearing his name. But some things are still unexplained. Could Hastings still be “H”?

For one thing, we know that he visited Lee Banks (Alastair Natkiel) at Blackthorn Prison to blow the cover of UCO John Corbett (Stephen Graham), with the opening salvo: “Sit down, fella. This b***ard’s got a thing or two to say to you. Trust me. You’ll be glad you did.” He told Banks there was a rat in the OCG, and the OCG soon worked out that rat was Corbett – and killed him. However, Hastings may have been either a) motivated by his personal hatred of Corbett for the assault on Roisin Hastings, or b) trying to get Corbett to take ‘refuge in a police station’ by blowing his cover and forcing him off the job. He also clearly felt guilty afterwards, giving £50k to Steph Corbett under the radar.

Next: When messaging John Corbett and Lisa McQueen, “unknown user” (who we presume is ‘H’) spelled “definitely” with an “a”. Later, Ted hijacked a conversation AC-12 were attempting to simulate between ‘H’ and the OCG via the same messaging system, writing that he could “definately pull the right strings”. Does the spelling error indicate that ‘H’ and Hastings are the same person? During the interrogation, Hastings’ defence was pretty shaky: he said he’d consciously mimicked the mis-spelling, which is not a fully believable answer. And now “definately” has reemerged in a message from the “unknown user” to Jo Davidson, telling her to “get rid of” Kate Fleming.

While using this messaging system and ‘pretending’ to be ‘H’, Hastings also repeatedly took matters into his own hands and ignored the suggestions of cybercrime expert Amanda (Rosa Escoda). He correctly guessed (or was it a guess?) that ‘H’ had never even known about the Palisade Shopping Centre meet-up (as it was a ruse from Lisa).

Also, we’re still doubtful about Ted Hastings’ real reasons for turning off his phone in season five so he was un-trackable, wrapping his laptop in bubble wrap, and taxi-ing to an electronics disposal shop to get it professionally destroyed. Hastings’ eventual confession that he was “looking at pornography” doesn’t really stack up, especially as we’ve seen his laptop open in his hotel room with a line of text popping up – just like the messages ‘H’ used to communicate with the OCG. If the porn was “nothing illegal, nothing extreme”, why go to such lengths to destroy the entire machine unless there was something else incriminating on there?

He then went rogue with a new plan to go “undercover” as ‘H’ – a plan which contravened all regulations, and completely ignored the fact that AC-12 had been taken off the case earlier that day.

It was Hastings who told Steve to respond to the “status zero” in the middle of the depot raid, ignoring the warning that it could be a trap and diverting the armed officers away from the OCG. Did he deliberately allow the balaclava gang to get away with £50m of stolen goods? And when Ted met the OCG at the nightclub and was taken to the warehouse, what would have happened if Miroslav hadn’t accidentally left his (traceable) burner phone on? Carmichael’s accusation does actually make some sense: “The net was closing in, your identity was slowly being unmasked. You’d reunited with the OCG in order to share in the profits of the Eastfield robbery.”

So, there are still some details that we’re puzzling over from season five, and it’s possible Hastings is not as straight-laced as he’d like everyone to believe. But in many ways, it makes absolutely no sense for Hastings to be “H” at this point – given how dedicated he’s been to his anti-corruption crusade, despite such strong opposition from so many quarters.

Plus, he is clearly not a rich man, and Mark Moffatt’s attempt to bribe him in season five made it clear that (at least as far as Moffatt knew) Hastings was not his ultimate big boss.

Is Patricia Carmichael H?

Anna Maxwell Martin plays Patricia Carmichael in Line of Duty

AC-3 boss DCS Patricia Carmichael (Anna Maxwell Martin) was brought in to investigate Ted Hastings in season five, and was ruthlessly determined to prove he is ‘H’ – although, just when she thought she had won, her case completely fell apart. And she’s now back in season six to take over AC-12 ahead of the Chief Constable’s upcoming merger, taking pleasure in cancelling the team’s ongoing surveillance operations (which have been deemed too expensive) and frustrating AC-12’s progress.

But is her desire to bring down Hastings and AC-12 motivated by malice – after they made her look foolish in season five? Is she driven purely by ambition, which is why she’s carrying out the Chief Constable’s orders without question – just proud of herself for getting a promotion? Or is she a bent cop… potentially even H?

It could also be Carmichael who ordered a member of her own team, PS Tina Tranter, to take Gill Biggeloe for a toilet break and then try to kill her. After all, she was the one who accepted Tina’s offer to deal with Gill, while she went down in the lift with Hastings.

Is Rohan Sindwhani H?

Ace Bhatti as PCC Rohan Sindwhani in Line of Duty

Police and Crime Commissioner Rohan Sindwhani (Ace Bhatti) was a new addition to Line of Duty in season five. He first entered the picture in episode two after asking to be “in on” a meeting between DCC Andrea Wise and Superintendent Ted Hastings, introducing himself to the AC-12 boss as they met for the first time – but despite his promises to fight police corruption, in reality he was happy to sweep things under the carpet. Why?

On meeting Hastings for the first time, Sindwhani – who is one of the police’s few elected officials – announced: “You’ll know I was elected to shake things up… for too long, the extent of police corruption has been covered up for fear of losing public trust.” But with the guidance of his senior legal counsel Gill Biggeloe, Sindwhani was actually happy to collude in downplaying the impact of “bent coppers” and protecting the reputation of the force.

Despite the mess that was Operation Pear Tree and the revelations about Gill Biggeloe, PS Tina Tranter, and a whole network of corrupt cops, Sindwhani gave the following public statement: “The Deputy Chief Constable and I are pleased to report Operation Pear Tree has completed a thorough investigation into institutionalised complicity between organised criminals and corrupt police officers. Its robust findings couldn’t be clearer. There is no institutionalised corruption in this police force.” This was entirely in bad faith.

However, Sindwhani seemed mainly to have been guided by Gill and used as a pawn in her game. She was calling the shots, making decisions on his behalf, and stepping in to choose John Corbett as Operation Pear Tree’s UCO because “The PCC required assurances that Operation Pear Tree was legally watertight.” Gill did not treat him like a fellow “H”.

In season six, he really seemed to have it in for Hastings. But then he resigned – telling Hastings that all the anti-anti-corruption decisions had been coming from the Chief Constable all along, and that he (Sindwhani) was actually fighting AC-12’s corner.

As he’s heading out the door, it doesn’t seem like Sindwhani is our “H”.

Is Andrea Wise H?

Elizabeth Rider plays DCC Andrea Wise

Detective Chief Constable Andrea Wise was another newcomer in series five, and her position of power within the police would certainly make her well-placed to be an ‘H’.

Throughout her time on the show, DCC Wise has been reluctant to support AC-12’s investigations, and only gave them access to Operation Pear Tree after Rohan Sindwhani (with Gill Biggeloe’s encouragement) asked her to take a “pragmatic approach” to Ted Hastings’ request. Later, she was the one to remove AC-12 from the investigation into Operation Pear Tree (perhaps to avoid them getting close to the truth?). She also ordered a separate inquiry into Hastings (perhaps in a bid to frame him as ‘H’?).

Like Sindwhani, DCC Wise seemed extremely keen to sweep police corruption under the rug, and paint the issue as a few isolated examples rather than a institutional problem. In a public statement at the end of the final episode, she said: “This constabulary will work tirelessly to root out rotten apples in its ranks.”

So DCC Wise could be “H”, but it’s more likely that she’s just averse to bad publicity.

Does H actually exist?

Line of Duty mystery person

Hastings is still convinced there’s still a “Fourth Man” (or woman) out there – the final “H” – who is a senior figure in the police force, working with organised crime and calling the shots in a network of corrupt police officers. This is all based on Dot’s dying declaration, and the supposed Morse Code clue.

But perhaps this is all one massive mix-up? Maybe “H” is a myth, after all? Or outdated information?

After all, it seems a little arbitrary who AC-12 has designated as an “H” and who they’ve decided is simply a corrupt cop. The three “H”-es they have so far are Dot Cottan, Gill Biggeloe, and Derek Hilton – but people like Hargreaves (Tony Pitts) and Patrick Fairbank only count as “corrupt cops”.

What point of seniority in the network do you need to reach, to be counted as an “H”? If Ryan had remained undiscovered in the police force, would he have worked his way up to becoming an “H”, or was he already there?

Plus, maybe Dot Cottan wasn’t aware of all the other “Dots” in the police force. Or maybe he meant four more “Dots”, after his imminent death. Or maybe he was just twitching his hand and AC-12 has got the wrong end of the stick completely.

Jed Mercurio, you’re messing with our heads.


Line of Duty continues on Sundays at 9pm on BBC One. Take a look at the rest of our Drama coverage, or check out our TV guide to see what’s on TV this week.