Before season six of Line of Duty began, fans were teased that guest lead DCI Joanne Davidson would be AC-12's most enigmatic adversary yet, and so far she has more than lived up to that billing.
Whenever it seems that viewers have started to work her out, another curveball is dropped – such as the identity of her mystery relative which was revealed last week, followed by her involvement in the incredible episode five cliffhanger.
So what is going on with her? What secrets lurk in her past? And most importantly, perhaps, what motivates her?
Having just laid out a whole bunch of questions, we do have a few facts to go on. So, to aid your speculating and theorising, here is everything we know about Jo Davidson so far.
Name: Joanne Davidson
From: Scotland. Kelly Macdonald uses her real accent for the role; the actress was born in Glasgow and grew up in Aberdeen.
Rank: Detective Chief Inspector, now Acting Detective Superintendent (after Buckells' arrest).
Date of birth: 22nd April 1979
Police background: Jo joined the police force on 29th July 1997, having trained at Melton Police College. Her training officer was C Stenhurst, who has never previously appeared in Line of Duty.
A month after Gail Vella's murder, she moved to Hillside Lane Police Station and joined Operation Lighthouse as SIO (Senior Investigating Officer), replacing the original SIO (DCI Billy McTulloch).
She has now been in that job for a year, and – until the events of season six – there had been virtually no progress on cracking the case.
Next of kin: Samantha Davidson, according to her personnel record – although we learnt in episode five that Samantha is apparently dead. This is particularly interesting because Jo told her ex-girlfriend PS Farida Jatri (Anneika Rose) that she had no family. And at Jo's flat, we've also seen a framed photograph of a younger woman and an older woman (possibly her and her mother?), which Jo used for target practice when she chucked her wine glass across the living room.
Mystery relative: At the end of episode four, showrunner Jed Mercurio left us on a cliffhanger with the revelation that AC-12 had found a significant DNA match for Jo Davidson.
“As we know, sir, officers’ samples are stored on the system to exclude contamination of crime scenes,” DI Steve Arnott (Martin Compston) told Superintendent Ted Hastings (Adrian Dunbar). “Now, an officer’s DNA isn’t speculatively examined on a routine basis, and certainly wasn’t back when Davidson joined the force. But because the DNA deposits detected at the house weren’t assumed to relate solely to a police officer, they were compared against the whole system. The analysis detected partial matches to a nominal whose DNA is stored on other police databases."
Of course, that mystery relative turned out to be none other than series one villain Tommy Hunter – the original leader of the OCG. And it doesn't end there: according to Arnott, Davidson's DNA returned “unusually high” runs of homozygosity – which suggests that she is possibly the result of in-breeding. This theory is given further weight when we consider a post-it note glimpsed in AC-12's offices that reads, “Jo Davidson’s DNA has been identified at Farida Jatri’s house. A match has been made to Tommy Hunter, stating she is both his niece and daughter.” It looks, then, as if Jo is the product of an incestuous relationship – although whether Samantha Davidson is Tommy's sister, or perhaps not actually Jo's birth mother, remains unclear.
OCG connection: For a while, we wondered if Jo could actually be "H" – the senior police figure who is the final lynchpin in a wide network of corrupt officers and organised criminals. After all, she's been doing an expert job of framing other people on her team (Farida; Superintendent Ian Buckells), and she's taken the Gail Vella case in the wrong direction whenever possible.
But now it's looking more and more like Jo is the one being pushed around, rather than doing the pushing. We've seen her go and collect a new burner phone from a shady-looking fella, and then have a screaming-crying fit in the car. We've seen her fail in her attempt to fire OCG mole PC Ryan Pilkington (Gregory Piper), who is now calling the shots. We've seen her attempt to quit working with the OCG (messaging "Job done. I'm finished"), and we've seen them deny her resignation.
It seems as if Jo is working with the OCG against her will - but the explanation for her motivation is still a mysterious. Is she being blackmailed?
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Relationship history: Until recently, Jo was in a relationship with a junior member of her team – Farida Jatri. In a conversation with DI Kate Fleming (Vicky McClure), she indicated that she'd just come out of a long-term relationship, but so far she's done everything she can to hide the fact that the partner in question was Farida. She's also told Kate, semi-cryptically, that she shouldn't believe the rumours.
It's possible that Jo is not "out" with her sexuality, or it may just be that she wants to keep her relationship with Farida private for other reasons.
Line of Duty continues on Sundays on BBC One. If you're up to date with the latest series, you can read our Line of Duty episode 4 recap here. Check out the rest of our Drama coverage, or take a look at what else is on this week with our TV guide.