Line of Duty welcomed prolific actor James Nesbitt to its stellar ensemble cast in series six, but it appears that his time on the show may be over before it began.
Episode six was another suspenseful chapter in Jed Mercurio's crime saga and ended with the bombshell revelation that retired copper and prime 'H' suspect Marcus Thurwell is dead (or so it seems).
His current home in Spain was raided by the local authorities, who were horrified to find two rotting corpses in the master bedroom, which were identified on the spot as Thurwell and his wife.
However, many Line of Duty fans aren't convinced with this verdict, arguing that its quite possible the former officer could have faked his own death in service to a grander plan.
It remains uncertain whether Nesbitt's mysterious character will make a full-fledged appearance, but he is nevertheless a key player in the climactic story of series six – read on for everything you need to know about him.
Line of Duty: Marcus Thurwell explained
If the name Marcus Thurwell rings a bell, it's probably because this isn't the first time that he has been mentioned as a suspect of OCG activity in the course of an AC-12 case.
Back in series three, Superintendent Ted Hastings and his team were looking into historic sexual abuse at a boys' home called Sands View, where DS Danny Waldron (Daniel Mays) had once been a resident.
They discovered that a social worker named Oliver Stephens-Lloyd had attempted to bring attention to the awful things going on there, but he was discredited and later turned up dead.
The investigation into his death was led by one DCI Marcus Thurwell and was ultimately ruled a suicide, but a second post-mortem brought about by AC-12 found signs that it could have been murder.
Briefly considered as a potential line of enquiry in the Danny Waldron case, research into Thurwell was halted when attention turned to his senior officer, Patrick Fairbank.
In the second half of series six Thurwell has become a person of interest once more. It was revealed that he may have obstructed the course of justice in the case of Lawrence Christopher's murder, which allowed his attackers to go free.
One of the perpetrators in that case was crime boss Tommy Hunter's son, Darren, which suggests that Thurwell could have been in cahoots with the OCG at this time.
Notably, we only saw Thurwell's name on paperwork in series three and we never saw a picture of his face, which allowed for the James Nesbitt reveal in this latest batch of episodes.
Is Marcus Thurwell 'H'?
In series five, we found out that the criminal mastermind known only as 'H' communicates with his associates via an encrypted instant message feed on a laptop, thus ensuring his complete anonymity.
AC-12 learned of this with some assistance from rogue UCO John Corbett and attempted to track down where the communication might be coming from.
In episode four, Cyber Crime's Amanda Yao informed Steve Arnott and Kate Fleming that attempts to trace the messages sent to the device revealed "another user with internet protocol [IP] address located in Spain".
Arnott points out that this finding doesn't necessarily mean the user is actually in Spain.
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"Correct," Yao replies. "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."
This brief interaction, which many fans will have likely disregarded by now, takes on a whole new meaning in light of Thurwell's newly uncovered wrongdoing, as the retired copper has been living in Spain for some time.
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As a result, it's quite possible that Thurwell is the one who has been communicating with his crime network via ominous text messages, from the relative safety of halfway across Europe.
However, episode six has cast doubt on that theory as Thurwell has been found dead in his home, suggesting that there could be someone in the OCG even more senior than him – the true identity of 'H'.
That's assuming he actually is dead, as many fans have pointed out that the bodies discovered could have been planted there in a conspiracy by Thurwell to fake his demise and avoid capture by the authorities.
The dimly lit scene and revolting decomposition of the bodies made it impossible for viewers to identify Thurwell themselves and, in the world of Line of Duty, it's best not to take everything at face value.
Line of Duty series six comes to an end with its seventh episode, making it perhaps the last opportunity for Nesbitt to show his face. We're not ruling anything out just yet. If you can't wait until next week, watch the Line of Duty finale trailer here now.