Line Of Duty finale: Kate Fleming and Steve Arnott aim their guns at a target ...

Line Of Duty's explosive series six finale is set to kick off on Sunday night, with avid fans (and AC-12 themselves) desperate to discover the identity of 'H'. 

But in a teaser snap from the final episode, DS Steve Arnott (Martin Compston) and DI Kate Fleming (Vicky McClure) could potentially have nailed the elusive fourth man as they point their guns at a target in a very tense looking scene.

Could the hunt for the devious criminal finally be over? 

Busted? In a teaser snap from the Line Of Duty finale, DS Steve Arnott (Martin Compston) and DI Kate Fleming (Vicky McClure) could potentially have nailed the elusive fourth man as they point their guns at a target in a very tense looking scene

Busted? In a teaser snap from the Line Of Duty finale, DS Steve Arnott (Martin Compston) and DI Kate Fleming (Vicky McClure) could potentially have nailed the elusive fourth man as they point their guns at a target in a very tense looking scene

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It's expected that 15 million viewers will tune in for the final episode, with the much of the plot centring around discovering the identity of 'H', with anti-corruption unit AC-12 having a big job on their hands in trying to catch the OCG villain. 

And by the look of determination on their faces, Kate and Steve look set to finally put an end to the mystery that has eluded them for months - but viewers will have to wait and see whether they do indeed have 'H' in their sights. 

DSI Marcus Thurwell (James Nesbitt) is reportedly Ladbrokes favourite to be unveiled as the antagonist with odds of just 7/4, with viewers convinced that the bent copper is still alive despite being declared 'dead' by Spanish officers in the last episode. 

Meanwhile, DCI Patricia Carmichael (Anna Maxwell Martin) has odds of being the villain of 2/1 according to Betfred. 

Caught at last? By the look of determination on their faces, Kate and Steve look set to finally put an end to the mystery that has eluded them for months - but viewers will have to wait and see whether they do have 'H' in their sights

Caught at last? By the look of determination on their faces, Kate and Steve look set to finally put an end to the mystery that has eluded them for months - but viewers will have to wait and see whether they do have 'H' in their sights

While a You Gov poll saw 22% of fans opt for chief constable Phillip Osbourne as their man, according to The Sun.

One thing's for sure, the identity of H will be revealed on Sunday as Alison Hammond announced H will be appearing on This Morning next week, while Phillip Schofield had earlier teased a 'very exciting guest'. 

The presenter, 54, signed off from Friday's episode of the ITV show teasing viewers that H will be 'on the sofa' on Monday, joking that she doesn't mean H from Steps.

After running through Monday's line-up, Alison told viewers: 'After Line Of Duty's Sunday night show we're going to have H on the sofa - and it's not H from Steps.'

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Her co-host Dermot O'Leary, 47, could not contain his excitement as he leant back and squealed at the exciting news.

On the case: It's expected that 15 million viewers will tune in for the final episode, with the much of the plot centre around discovering the identity of 'H', with anti-corruption unit AC-12 having a big job on their hands in trying to catch the OCG villain. 

LINE OF DUTY: WHO IS THE FOURTH 'H'?

Line Of Duty creator Jed Mercurio excited fans when he shared the first clue about the plot of season six to Twitter.

Uploading a snap of a packet of the Australian chocolate biscuits TimTams with the caption '#LineofDuty Series 6 Plot Clue No. 1', fans began to ferociously speculate as to what it might mean.

But one plot point hanging over the next season of the show is about the identity of the ominous 'H'.

While the mystery was somewhat answered in the season five finale, it was also revealed that there are FOUR people pertaining to be 'H', with the final one still unknown.

So who could it be?

Patricia Carmichael (Anna Maxwell Martin)

Patricia Carmichael (Anna Maxwell Martin)

Patricia Carmichael (Anna Maxwell Martin)

She was one of season five's stand-out characters, swooping in towards the end of the series to interrogate Ted Hastings - highly suspected to be 'H' at the time.

And while she simply seemed to be excellent at her job - and hellbent on uncovering the corruption within the department - could it be that Patricia Carmichael was SO keen to pin the blame on Ted to take the focus away from herself.

Could SHE be the fourth 'H'?

Her position of power and respect, along with her unnaturally steely and cut-throat demeanor, could well point to this.

Ted Hastings (Adrian Dunbar)

Ted Hastings (Adrian Dunbar)

Ted Hastings (Adrian Dunbar)

Ted Hastings was pinpointed by viewers of the show, as well as the characters on the show, to be a candidate for 'H'.

But it seemed he was exonerated by the end of season five, allowed to walk free.

But could be potentially be triple-crossing us all? Could he in fact STILL be the potential fourth 'H'.

The biggest issue with this theory is that Gill Biggeloe - one of the three revealed to be 'H' - was so against him. Surely she wouldn't be working to deter him if they were in league?

UNLESS, she doesn't KNOW he is the fourth 'H'?

DCC Andrea Wise (Elizabeth Rider)

DCC Andrea Wise (Elizabeth Rider)

DCC Andrea Wise (Elizabeth Rider)

Detective Chief Constable Andrea Wise was new to the show in season five and is another high-powered contender for 'H'.

She has been constantly interfering when it has come to supporting AC-12’s investigations, removing them from the investigation into Operation Pear Tree. She also instigated the Ted Hastings investigation.

She is also keen to cover up police corruption, despite announcing at the end of season five: 'This constabulary will work tirelessly to root out rotten apples in its ranks.'

PCC Rohan Sindwhani (Ace Bhatti)

PCC Rohan Sindwhani (Ace Bhatti)

PCC Rohan Sindwhani (Ace Bhatti)

Police and Crime Commissioner Rohan Sindwhani demanded to be 'in on' a meeting between Andrea Wise and Ted Hastings. This might be a small clue but any clue could be valid at this point.

Any shady behavior suggests 'H' is at play, and so Rohan could indeed be culpable.

 

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Meanwhile, the publication reports that the preview episode of the finale has been shrouded in secrecy by the BBC, with TV insiders and journalists given a plethora of passwords to access the show. 

A source said: 'Staff were under strict instructions to keep character and plot revelations under strict lock and key.

'Friends and families of the key actors also kept schtum on letting slip on any show details.'

Hush hush: Meanwhile, the publication reports that the preview episode of the finale has been shrouded in secrecy by the BBC, with TV insiders and journalists given a plethora of passwords to access the show

Hush hush: Meanwhile, the publication reports that the preview episode of the finale has been shrouded in secrecy by the BBC, with TV insiders and journalists given a plethora of passwords to access the show 

The final of Line Of Duty looks to be an action-packed finale episode complete with a police standoff, the return of balaclava men and the discovery of a written note with THAT 'definately' misspelling.

A new trailer sees Superintendent Ted Hastings (Adrian Dunbar), who is facing imminent retirement, state: 'All of these suspicious deaths were orchestrated by one officer in particular, H. The fourth man.'

Hastings' powerful words went alongside flashbacks of the deaths of solicitor Jimmy Lakewell, police officer Lisa Patel, journalist Gail Vella and former Detective Inspector Marcus Thurwell- whom fans believe is still alive.

Trailer: In a teaser released on Monday, viewers can be certain of an action-packed finale episode with a police standoff, the return of balaclava men and that 'definately' misspelling

Trailer: In a teaser released on Monday, viewers can be certain of an action-packed finale episode with a police standoff, the return of balaclava men and that 'definately' misspelling

AC-12: The trailer starts off with Superintendent Ted Hastings (Adrian Dunbar), state: 'All of these suspicious deaths were orchestrated by one officer in particular, H. The fourth man'

AC-12: The trailer starts off with Superintendent Ted Hastings (Adrian Dunbar), state: 'All of these suspicious deaths were orchestrated by one officer in particular, H. The fourth man'

The trailer then shows acting Superintendent Jo Davidson (Kelly MacDonald) leaving the high-security prison in handcuffs, only to end up alone in a van with a corrupt prison officer who previously injured Lindsay Denton in series three.

A handwritten note is also teased in the trailer, with the word definite misspelt to mirror what viewers have seen previously. 

A huge clue of the identity of H began to emerge in series five, when the OCG communicated with 'H' through a computer.

Fall from grace: The trailer then shows acting Superintendent Jo Davidson (Kelly MacDonald) leaving the high-security prison in handcuffs

Fall from grace: The trailer then shows acting Superintendent Jo Davidson (Kelly MacDonald) leaving the high-security prison in handcuffs

Clue: A handwritten note is also teased in the trailer, with the word definite misspelt to mirror what viewers have seen previously- will this be the clue AC-12 needs?

Clue: A handwritten note is also teased in the trailer, with the word definite misspelt to mirror what viewers have seen previously- will this be the clue AC-12 needs? 

Eagle-eyed fans were quick to notice H

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