'Line of Duty' 6.04 review — blood relatives, shock deaths and deleted emails

Line of Duty delivered fans a real treat this week, because episode four of Line of Duty Season 6 had it all — high drama, shock deaths and a cliffhanger ending that is going to keep viewers speculating until 9pm next Sunday evening, 

But as always Jed Mercurio and his team have left us with many unanswered questions to keep us awake at night. Here's our list of five HUGE questions after Season 6 episode 4... 

Who is Jo Davidson related to? 

Now that's what we call a cliffhanger ending! The revelation that Joanne Davidson is related to someone whose DNA is kept on police records will have fans around the country trying to work out who it is Jo shares a family tree with.

Could it be Steve Corbett? Is that why Jed has brought his wife Steph Corbett back for Season 6? Or is it someone from further back in Line of Duty history? Jed is famous for bringing long-forgotten characters back to the forefront of fans minds, could Jo's long lost relative be from Seasons 1 or 2? 

And what side of the law is Jo's blood relative on? Could the fact she is being blackmailed by the OCG or a corrupt leading officer be because she is related to them? Does she share DNA with Ryan Pilkington? Former OCG leader Tommy Hunter? Or even Lee Banks? 

Is Kate starting to realise Jo is up to something? 

Until now Kate Fleming (Vicky McClure) has always seen the best in Jo Davidson. The pair clearly get on, sharing cosy chats over a glass of Sauvignon or two, but this week was the first time that Jo gave Kate a real reason to doubt her. 

Despite Steve Arnott's (Martin Compston) desperate attempts to get Kate to see Jo is hiding something, Kate has always maintained her boss's innocence, even worrying about her safety and giving her the heads up that Ryan Pilkington has been following her. 

However, when Kate confronts Jo over Ryan's shady antics, Jo still had Ryan's words of warning ringing in her ears and set Kate straight once and for all by hinting that she would use that fact Kate was following the police patrol car that was supposedly taking Terry home and didn't call for backup until the vehicle was in the reservoir. 

Will this flash of Jo's darker side make Kate sit up and take note? After being warned by Ryan that Jimmy Lakewell's cause of death was 'being a rat', Jo will clearly go to any lengths to keep her secret safe. But will her lies leave Kate in danger?

What fresh drama will Lee Banks bring? 

He's back! The last time we saw Lee Banks was at the end of Season 5 when Ted Hastings (Adrian Dunbar) went to visit him in HMP Blackthorn. While we still haven't had clear confirmation on what Ted was there to say to Lee in prison, it has been heavily hinted that Ted was the one who outed John Corbett as being the undercover police officer in the OCG. 

Lee might still be serving time at Her Majesty's Pleasure, but that doesn't stop him working for the OCG from the inside. Not only does he appear to have many prison staff working undercover for organised crime, but he also taught DCU Ian Buckells what happens to a rat by killing Jimmy Lakewell in front of him. Something tells us this isn't the last we have seen of Lee. 

Will Superintendent Ted Hastings really leave?

Everyone knows Line of Duty just wouldn't be the same without Ted Hastings, but Jed Mercurio is also renowned for not being afraid to get rid of big names in the show, meaning no one is safe - not even Ted. 

Could Ted really be retiring at the end of Season 6? Or will AC-12 manage to pull something out of the bag in the anti-corruption investigation on Jo Davidson and Ian Buckells and work out who has got the pair of them right where they want them? If they manage to crack the case, could it be enough to save Ted's job and AC-12?

When will Steve Arnott read his email from Occupational Health? 

Following his not-so-random drugs testing in Season 6 episode 3, something in his results has clearly caught the eye of occupational health. Whatever they have found is obviously a pressing matter considering the urgent nature of their email, but how much longer can Steve go on just deleting the messages? Have they uncovered his painkiller addiction? Or is there something else that has been flagged up by the results? 

• Who is H?
• Tony Gates
• DS Chris Lomax

Line of Duty continues on Sunday nights at 9pm on BBC One. You can catch up on past seasons and missed episodes on BBC iPlayer.