After an action packed episode last night, Line of Duty fans have picked up on another Easter egg which might help uncover the answer to the question that has been hanging over our heads for the last few weeks: who is 'H' – or, should we say, who is the fourth corrupt officer?
In a covert meeting between DI Kate Fleming (Vicky McClure) and head of AC-12 Ted Hastings (Adrian Dunbar) in episode four of the series, the letter 'H' can quite clearly be seen spray-painted on the wall in the background. Coincidence? Quite possibly.
Despite Steve Arnott (Martin Compston) deducing at the end of season five that what Dot Cotton (Craig Parkinson) was referring to in his dying declaration was, in fact, a fourth man, fan theories about the significance of the letter 'H' have remained unabated.
First there was DI Arnott flashing his lights four times in episode one, and then there were Steph Corbett's (Amy de Bhrún) mysterious H-shaped kitchen tiles in episode three. So what do all these hidden 'H's' mean?
Jenny Ryan of The Chase pointed out that the writers have gone to quite some effort this season to toy with with the show's ever more attentive viewers with these H-related Easter eggs.
Speaking to Radio Times, director Jed Mercurio previously admitted: "If you have created a set of mysteries, you also have to understand the significance of misdirection and red herrings. So we do use misdirection at times, and it’s deliberate.”
At this point, tracking down 'H' is like trying to find a needle in a haystack. Or maybe a Hasting?
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Suspicion has enshrouded the battle-hardened superintendent Hastings since series five, when his misspelling of the word "definitely" as "definately" appeared to match that of 'H'. Perhaps he is not following the law quite to the letter after all.
And even the seemingly scrupulous DI Fleming has come under suspicion from fans with some suggesting that she may in fact be DCI Joanne Davidson’s (Kelly Macdonald) long-lost sister. (More on who Jo Davidson's mystery relative is here.)
What's more, the tunnel with 'H' spray-painted on its wall resembles the same covert meeting spot AC-12 have been using for several seasons. Initially, for Kate to meet with Dot. Then, for Kate to meet with Steve Arnott. And now, for Kate to meet with Hastings. Who is the common denominator here? You guessed it.
While Line of Duty creators appear to be having a bit of fun with the fans this season, all we can do is diligently keep an eye out for clues and wait with anticipation for next week’s episode.
Line of Duty continues Sunday at 9pm on BBC One. If you're looking for more to watch, check out our TV Guide or visit our Drama hub for all the latest news.