Plus: The best Line of Duty fan theories

Warning, Line of Duty spoilers are ahead.

We’re just hours away from Line of Duty’s final episode of the season and what could be the show’s final episode ever.

The sixth series follows AC-12 on their mission to hunt down the ultimate bent copper – known only as ‘H’ or the Fourth Man.

This series Scottish actress Kelly Macdonald joined the cast as the enigmatic detective Joanne Davidson.

Her character has been central to the mysteries of the season, with Steve Arnott (Martin Compston) and Ted Hastings (Adrian Dunbar) trying to decipher if she is secretly working for the organised crime group (OCG).

In episode six, Jo is brought into the iconic AC-12 interview room.

It is in this interrogation where – despite saying “no comment” a whopping 34 times – her poker face finally starts to crack.

Macdonald has been praised for her performance as Jo, who is visibly shaken when Steve Arnott starts asking about her mother’s suicide.

He then reveals the identity of Jo’s biological father from a DNA match. Crime boss Tommy Hunter was Jo’s uncle and also her father.

She is clearly shocked by this revelation, denying it and bursting into tears.

Eventually Jo opens up and says her mother told her she was raped at the age of 15 and forced to go ahead with the pregnancy.

Here are the most likely suspects who could be ‘H’.

Marcus Thurwell

James Nesbitt has what seems like a small cameo in Line of Duty as Marcus Thurwell.

In the latest episode, a police raid at his Spanish home appears to show him and his wife discovered dead – though fans have their suspicions. Back in season three, DCI Thurwell is said to have investigated the death of Oliver Stephens-lloyd, a social worker who died after threatening to highlight the abuse at Sands View boys’ home.

And it was implied he perverted the cause of justice in the racist murder of Lawrence Christopher – one of the attackers was Tommy Hunter’s son.

Thurwell moved to Spain, which is where the OCG messages to Jo’s laptop have been coming from.

When asked her relationship to him, Jo looks distressed, and says “no comment”. But could it be too obvious?

Philip Osborne

He’s been a villain since series one, when he tried to get Steve Arnott to lie about killing an innocent man in a bungled anti-terrorism operation.

Throughout the show Osborne’s risen up the ranks and is now Chief Constable – or, as Ted Hastings puts it, a “bare-faced liar promoted to our highest office”.

But when he was an inspector, Osborne was also involved in the inquiry into the murder of Lawrence Christopher. It’s certainly plausible that he is ‘H’, and Jo’s adopted dad.

Mike Dryden

Remember him? The disgraced Deputy Chief Constable from series two. He was played by Edinburgh actor Mark Bonnar, so there is the Scottish link to Davidson.

Derek Hilton

Assistant Chief Constable Derek Hilton met a grisly end in series four when he was found shot in the mouth in a staged suicide by the OCG.