Few shows have kept audiences guessing quite as much as Line of Duty, and season six has provided a bumper year as the show looks close to revealing who the mysterious ‘H’ is.
The BBC police thriller has continued to shock audiences for years with its twists and turns, but show creator Jed Mercurio is known for hiding little details within the series that may or may not be linked to the final outcome.
The latest episodes have kept viewers on their toes regarding the future of AC-12, and whether they will ever have the time to find out the truth behind police corruption and organised crime.
So from pen tapping morse code to fake deaths, here is a selection of some of the best fan theories ahead of the Line of Duty series six finale.
Grammar error on poster
Although only a minor detail, some viewers are determined that one little grammatical error could tie up the mystery behind several typos associated with ‘H’.
In episode five of season six, fans spotted a poster on the wall behind Acting Detective Superintendent Jo Davidson (Kelly Macdonald).
The sign read: “Please return all files once your finished with them Thank you!!!!"
Some viewers noted the misuse of the word “your”, believing it could be a major clue.
They believe the grammatical error links to the collection of other typos made by a mysterious OCG person who has been communicating with Davidson via her laptop.
Fans think the error on the poster could indicate the shadowy figure could have been the one who put up the poster in the station.
Whether it is H behind the poster or not - Line of Duty loves to chuck in a spelling error to confuse fans.
Carmichael’s morse code with her pen
Considering the sheer variety of fan theories, even this one is a bit leftfield.
After the tense interrogation scene between DS Patricia Carmichael (Anna Maxwell Martin) and DS Jo Davidson in episode six, some viewers believe they found a secret hidden message connecting Carmicahel to ‘H’...all by the click of her pen.
During the chat, Carmichael was seen tapping her pen four times on the table - which has led to some fans speculating she was actually using morse code.
One viewer noted on Twitter: “Whilst interviewing Davidson, Carmichael taps her pen on the table 4 F*****G TIMES!! We all remember Dots message when dying, 4 Dots .... 4 taps in Morse code? F*****G H!!!"
Marcus Thurwell is still alive
Episode six set up a tense finale to the season after it revealed that one of AC-12’s prime suspects was found dead in his home in Spain.
In the final minutes the team at AC-12 gathered round the computer to watch Spanish police officers raid Marcus Thurwell’s (James Nesbitt) last known location in Spain.
However, at the end of the search bodycam footage showed two corpses in the premises, with the officers saying that they were “Mr and Mrs Thurwell”.
Some fans believe that Thurwell is in fact still alive, and wasn’t killed off by the show within 70 seconds.
Eagle-eyed viewers noticed some familiarities between one of the Spanish police officers who took part in the raid - and even went so far to claim that one of them is in fact Thurwell himself.
A screengrab posted online saw fans examine the likeness to Thurwell, especially his eyebrows and eyes.
Anna Maxwell Martin’s Instagram spoiler
Anna Maxwell Martin added another layer of suspicion on to her character DS Carmichael after a post on her Instagram account.
DS Carmichael was brought into AC-12 to shake things up, and seemingly speed up Superintendent’s Hastings’ imminent retirementment.
Throughout Line of Duty one huge clue has remained constant - ‘H’ has the inability to spell definitely, instead writing ‘definately’.
On Instagram, the actor posted a picture of her dog with the caption ‘Definately mama to this bank drain’.
The spelling mistake led fans to instantly pose the question of whether this was a cryptic clue from Martin regarding her character’s possible links to organised crime.