Jed Mercurio’s BBC drama broadcast its fourth episode of series six on Sunday (11 April), and it ended with a revelation that will keep fans busy until the next one airs.
Ahead of the episode, Martin Compston, who plays DI Steve Arnott, had hinted that the particular instalment could go down as one of the biggest in the show’s history.
*Spoilers follow – you have been warned*
The episode ended with the discovery that DCI Joanne Davidson (Kelly Macdonald) is related to a character known to fans.
Arnott revealed the news to Superintendant Ted Hastings (Adrian Dunbar), and handed him a file featuring the details of the person who is “identified over the page”.
The revelation is so big that it prompted Hastings to exclaim the immortal quote, “Mother of God”, before the episode came to a dramatic end.
We know it’s a male character, as Arnott refers to the unknown person as a male but, whose face was on that page?
Fans were quick to say they think the mystery person will be revealed to be John Corbett, the undercover cop played by Stephen Graham in the last series.
Corbett was killed by Ryan Pilkington, who, following the latest episode, is now controlling Joanne with ominous threats on her MIT squad.
The revelation would back up the theory that the woman pictured in the photo with Joanne in her home – presumed to be her mother – is Corbett’s mother, also.
Another character it could be is Tommy Hunter (Brian McCardle). While the relative doesn’t necessarily have to be Scottish to be related to Joanne, Hunter being Scottish certainly works in this theory’s favour.
Hunter, a paedophile, was the leader of the Organised Crime Syndicate and is the one who groomed DI Matthew Cottan (Craig Parkinson) to be his man on the inside within AC-12.
Could Hunter actually be alive? If so, is he the mystery person Davidson is speaking to on her laptop?
It’s worth noting that, going by Tommy’s biography on the Line of Duty Wikipedia page, that would have made him 13 at the time of her birth.
Naturally, some fans have name-checked the other Scottish character to have appeared in previous series: former Deputy Chief Constable of Central Police Mike Dryden (Mark Bonnar). It certainly wouldn’t do Joanne any favours to be revealed as Dryden’s relative, considering he’s currently serving a suspended sentence for perverting the course of justice.
One theory is that Joanne could actually be the sister of DI Cottan, which would match with Hastings’ reaction considering how closely the pair worked together before he was revealed to be corrupt in the third series.
Perhaps Joanne was also groomed by Hunter? Either way, this twist would make it hard for the DCI to evade suspicion from AC-12 in future episodes.
The fact that Davidson has tried to brush her family history under the rug since the first episode probably means the person is going to be somebody with strong ties to police corruption.
Elsewhere in the episode, the show’s viewers think that a possible off-screen moment hinted at a future Steve Arnott revelation.
Line of Duty continues on BBC One on Sunday (18 April) at 9pm with an episode that sees the surprise return of a former character.
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