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But one fan is well ahead of the rest, having put together a huge evidence board in her quest to find out who is behind the criminal moniker.
In the spirit of It's Always Sunny in Philadelphia, Katie Rogers, from Dorset, pinned photos and notes, linked by thread, to a massive board to help organise her thoughts.
According to reports, the mum-of-three is so dedicated to the cause that she has watched each episode of the current series a whopping five times, taking down notes and analysing every scene.
And speaking to The Times, the 40-year-old says it has helped her spot things most would miss.
She said: "The show is so great and interactive.
"Over the last 12 months [of lockdowns] we've got more and more disconnected and not been able to see people and this has brought us back together.
"I think I speak to my family twice as much since the show started compared to before."
In another interview with Metro, Katie admitted that she hasn't always been a fan of the show.
However, she says she was hooked as soon as she started, and just loves playing amateur detective.
"I joined it about series three and discussing theories just made me get more into the nitty gritty of it," she told the publication.
"I think when you watch another series, you have to watch it all from the very beginning again because it all ties up."
But while you might expect diehard fans of the series to have a go at working out who is behind the infamous OCG, one person you wouldn't is rapper and music producer Drake.
However, some believe the artist might, in fact, know H's true identity.
The photo posted to the Canadian's Instagram account shows Drake, with fellow rapper Giggs and head of security and friend Chubbs.
The 34-year-old has mysteriously captioned it 'H', leading Line of Duty fans to make the link between him and the BBC crime drama.
And while it seems extremely unlikely that Drake knows insider Line of Duty secrets, we don't have long to wait until we know who H actually is.
The feature-length episode will air at 9pm on Sunday (2 May). Will we find out who the 'fourth man' is? Let's hope so.
Featured Image Credit: Katie Rogers
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