It draws an audience of millions every week so it's no wonder Line Of Duty viewers will spot something that doesn't seem right.
And that was the case during Sunday night's episode as fans spotted a massive blunder at the start of the programme.
Undercover copper John Corbett, who is posing as a gang leader, was getting orders from the mysterious boss of the criminal organisation.
The big baddie was worried about John's plan to target Eastfield Depot, which is used by the police to store confiscated drugs and weapons.
On the laptop they use to communicate with the higher levels of the OCG, a message read: "Eastfield depot is definately high risk."
The corrupt cop at the top of the chain asked John is they payout was high enough, but had made a bit of an embarrassing spelling error.
Line Of Duty viewers called the blunder out on Twitter but many pointed out that it could have been intentional.
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One fan asked: "Ya see that spelling mistake? 'Definately' from 'Unknown caller' - that's going to identify someone later on"
"Ooh. Spelling. “Definately”. That’s important," added another.
A third said: "I hope that misspelling of definitely was intentional?! #definately"
"Now trying to desperately remember who might have spelt ‘definately’ on a board somewhere - not that I see clues everywhere of course," said a fourth.
John tried to reassure the big boss that his cunning plan would work.
His associate, Lisa McQueen, asked if there were any separate orders for her.
A message came back saying that she "knew what to do", prompting some fears from John over the identity of 'H'.
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Who do you think is 'H'? Let us know on Facebook and Twitter.
Line of Duty creator Jed Mercurio has being teasing fans with the identity of 'H'.
Mercurio has revealed he has been planning a shocking twist since the show began.
Viewers have been comes up with theories and attempting to predict who 'H' really is - but Mercurio has explained he could change his mind.
He revealed he has given several characters names that can be turned into 'H, so there are a fair few suspects.
The show's creator told the BFI & Radio Times Television Festival: "I suppose if I had an idea later on that was even better then, yeah, of course I would change it.
"Because you want it to be as good as possible and surprising and so forth."
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He added: "Sometimes there were characters whose name could be corrupted or nicknamed into being an 'H' if I wanted to.
"Some of the characters were given names where they could have been revealed as having an 'H' connection if it was required."
*Line Of Duty airs Sundays on BBC One at 9pm
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