Line of Duty fans have LOTS of theories about Lisa McQueen, 'H' and the word "definately" after the shocking end to episode four

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*Spoilers for Line of Duty series five episode four to follow*

Episode four was very eventful. It kicked off with the revelation that John Corbett (Stephen Graham) had tortured Hastings' wife in order to procure information about the AC-12 top dog that might expose him as corrupt. Then, after a failed attempt to capture Corbett, during which Steve Arnott (Martin Compston) ignored Hastings' order to shoot and kill the undercover officer, Lisa McQueen had Corbett killed, after deducing she was the rat in the OCG (Organised Crime Group).

Along the way, we also saw the return (of sorts) of series one's Jackie Laverty (Gina McKee), Hastings implicating himself as 'H' by spelling "definately" incorrectly in the same way, taking in a bag of cash and visiting incarcerated OCG member Lee Banks, and Gill Biggeloe being generally suspicious.

Viewers on Twitter have plenty of ideas about what is going on.

First and foremost, they reckon that Lisa McQueen is in fact an undercover operative as first suspected, after she broke down in tears following Corbett's murder.

"Lisa is working undercover for Hastings," @EllieMBond posited. "He spelt 'definitely' wrong so she knew it was him giving the order to 'bring this to a close'."

Another suggested she might be the daughter of Tony Gates (Lennie James' character from series one), but we're not so sure those timelines add up...

https://twitter.com/EllieMBond/status/1120071448989712387

https://twitter.com/mrdanwalker/status/1120097949105774595

https://twitter.com/scouseweegian/status/1120069622152278016

https://twitter.com/Cromwell606/status/1120075560602959873

https://twitter.com/ballydonna/status/1120069675818287105

Others reckon that because Hastings spelled 'definitely' wrong, he must be 'H'.

"I'm now sure Hastings is #definately corrupt," Rob Little wrote. "Lisa's reaction to his last message how he wanted it finished and Corbett being killed off is no coincidence. Add to that Hastings getting his laptop destroyed in episode three and the bribe tonight..."

https://twitter.com/robjlittle_/status/1120072864034709504

https://twitter.com/girl_on_fire725/status/1120067867012141058

https://twitter.com/missleonie/status/1120067363448262656

And lots of people now reckon that Gill Biggeloe is 'H'. There isn't much to back this up as of yet, but it probably has to do with her rather unseemly power-play tactics in seducing Ted, and her previous suggestion that the right amount of bent coppers to catch is 'some' and not 'all'.

https://twitter.com/RadioTimes/status/1120073889256812545

https://twitter.com/richardhowle/status/1120072866257670150

https://twitter.com/alarter/status/1120083384150130690

https://twitter.com/ANNIET34/status/1120063207018848257

Is it next Sunday yet?

Line of Duty series five continues on Sunday at 9pm on BBC1