The fan theories are flying all over the places this series.

Eagle-eyed Line of Duty fans have spotted the reappearance of a familiar prison guard from a previous series of the BBC drama. And, shock, she's a bent copper. Before going any further, if it wasn't already clear: spoiler warning. In Sunday's episode, Farida Jatri, the character who first raised suspicions about the behaviour of DCI Davidson, is called in for questioning by AC-12. However the prison guard who goes to collect her breaks Jatri's wrist so that she has to go to the prison hospital and cannot attend the interview. This wasn't the first time that the guard in question, Alison Merchant, had appeared in the show. It also wasn't the first time that she'd been involved in some pretty grim acts. Pearson appeared in series two, when she attacked Lindsay Denton to stop her talking to Hastings and co. In this series, she poured boiling water on Denton's hands and mixed her food with faeces. So she's real good egg. After this she was replaced and had not been seen again. Until now of course. So it seems like she's another bent copper who's part of the pesky OCG that have been making the lives of Steve Arnott, Kate Fleming, and Ted Hastings such hell over the past few years. It's just another of a number of references and call-backs to previous series that we've seen since the show's return. After a slow-burner of a start as pieces were put in place, based on the last episode it looks like the scene has now been set for an explosive storyline, which could see a number of strands and storylines come together and reach their conclusion. I think we can also all echo the sentiments of one Reddit user though, who simply asked "can we see these prison guards getting their comeuppance this season please?" That would be satisfying.