Mother of God! Who is DCI Jo Davidson's mystery blood relative in Line of Duty?

When forensic officers harvested Davidson’s DNA from her ex-lover Sergeant Farida Jatri’s house, it closely matched someone else whose DNA was already stored on the police database – meaning that dodgy Davidson and this as-yet-unnamed individual are blood relatives. Even diesel-sucking Supt Ted Hastings looked rattled when he looked inside the folder and discovered their identity.

Who could it be? What could it mean? Well, let's run through the potential candidates. For the benefit of the DIR, of course, this is mere speculation and writer Jed Mercurio might have other ideas…

John Corbett

Series five’s rogue undercover cop, DS John Corbett (Stephen Graham), had a vendetta against Hastings which was traced back to the Troubles. In his early days as a young RUC officer, Hastings had grown close to Corbett’s birth mother, Anne-Marie McGillis, who was promptly murdered by paramilitaries for being a police informant. Could Corbett have had a long-lost sister who was also adopted on the British mainland and became a police officer?

Back in episode one, Davidson angrily threw a full wine glass (wasteful) at a framed photo of her mother, who bore a distinct resemblance to McGillis. The camera lingered on the snap, which might be a clue. Is Jo, like brother John, motivated by avenging Anne-Marie? Or even paying back John’s killer, who happens to be Ryan? Perhaps she plans to take down the OCG from the inside.

A link to Corbett might also explain the return of his widow Steph Corbett (Amy De Bhrún) this series, complete with her Jiffy bagful of guilt money from Ted. (Large denomination notes only. No coppers, bent or otherwise).

Jackie Laverty

Aka “Tony Gates’ bit on the side”, according to old charmer Ted. Property developer Jackie Laverty (Gina McKee) was the wealthy mistress of Line Of Duty’s first ever antagonist, DCI Anthony Gates (Lennie James). Laverty had a sideline in laundering money for organised crime until “Balaclava Men” slit her throat for her silence and to obtain leverage over Gates.

The OCG kept Laverty’s deep-frozen corpse at the flat of cuckooed Terry Boyle (Tommy Jessop) for seven long years. They finally dumped her body alongside Corbett’s last series. AC-12 just found the freezer, hastily removed from Terry’s flat, with traces of Laverty’s blood still inside - proving a connection between journalist Gail Vella’s unsolved murder and the OCG.

Could the resurfacing of the Laverty plotline also be paving the way for a plot twist that Davidson is her younger sister or half-sister? The brunette McActresses look faintly similar, after all.

Tommy Hunter

Line Of Duty’s original “big bad” was gangster Tommy Hunter (Brian McCardie) - the well-connected kingpin who’d groomed The Caddy (later revealed as Craig Parkinson's DI Matthew "Dot" Cottan) since his teens. Hunter was killed by his criminal associates in series two after entering witness protection. As the OCG’s original leader, it was he who first used “Balaclava Men” as his thuggish enforcers and established a network of bent coppers to do his dastardly bidding.

Hunter might be long dead, but could Davidson be his illegitimate daughter? They’re both Glaswegian, for a start. She’d be about the right age and obviously has issues with her parentage - hardly surprising if her father was a wrong’un like Hunter. She snapped to Farida that she “didn’t have a family”, which might be because she’s ashamed of hers.

That familial connection could be how Davidson got embroiled with the OCG or embedded within the police force in the first place. She apparently wants out but perhaps villainy is in her blood. A link to Hunter would also be a neat dramatic device, taking Mercurio’s tangled web of corruption back to the very beginning. Maybe Hastings is fighting an old battle, like he said.

Danny Waldron

Might Davidson be related to Sergeant Danny Waldron (Daniel Mays), the armed response squad leader who survived just a single episode of series three? Well, Danny did grow up in care, so presumably never knew his birth family. The Sands View boy’s home paedophile ring, of which Danny was a victim, has already been mentioned this series as among the scandals being investigated by Gail Vella when she was assassinated.

Danny and Jo would be around the same age (actors Mays and Macdonald are two years apart). They could have been separated in childhood and sent to different care homes or foster families. Both are troubled and volatile as a result of their upbringing. It’s just about possible, fella.

Kate Fleming

Who was the only member of the Line Of Duty dream team missing when the DNA match was found? DI Kate Fleming (Vicky McClure). Is this significant? Probably not. Still, Kate being her boss’s long-lost little sister would be a head-spinning development.

Many viewers have speculated that Kate will play a pivotal role this series. It would also put a queasy new spin on the hints of sexual attraction between the pair.

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Denton, Dot or Gill

Could Davidson secretly be the little sister of series two antagonist DI Lindsay Denton (Keeely Hawes)? Or DI Matthew “Dot” Cottan (Craig Parkinson), the string-pulling inside man codenamed The Caddy? Or eyelash-fluttering femme fatale Gill Biggeloe (Polly Walker), the police lawyer who was unmasked as corrupt in the series five finale?

Rule nothing out at this stage *narrows eyes suspiciously in direction of Jed Mercurio’s computer keyboard*.

Ted Hastings

OK, now we’re getting carried away. Or are we? Ted clearly has a murky past from back in Belfast, not to mention a chequered romantic history. When the sly old silver fox uttered a trademark “Mother of God” at Davidson’s DNA report, how close to home was it?

It would be one helluva rug-pull if the AC-12 gaffer turned out to be investigating the love child he never knew he had. Perhaps he did float up the Lagan on a bubble after all.

• For the latest news and expert tips on getting the best deals this year, take a look at our Black Friday 2021 and Cyber Monday 2021 guides.

Line of Duty continues on Sundays at 9pm on BBC One. If you're up to date with the latest season, why not read our Line of Duty episode 4 recap. Take a look at the rest of our Drama coverage, or check out our TV guide to see what's on TV this week.