The British crime drama has a reputation for major rug-pull twists and palpitation-inducingly tense interrogations – and it’s going even bigger in Series 4.
With a new channel, impressive cast additions and more, here are six things you need to know.
1) It’s moved to BBC One
Line of Duty is an outright BBC success story – after three critically-adored series on BBC Two, the show is making the step up to a Sunday night 9pm slot on BBC One.
While it’s a bigger platform for one of the nation’s best-reviewed TV shows, creator and writer Jed Mercurio has promised fans that the series won’t be changing much.
“In the discussion that was had about the show moving it was made clear that nothing needed to be done differently,” he says. “We’re very pleased to be sharing a platform with some of the other acclaimed and successful dramas already on BBC One.”
2) It’s set one year after Series 3 ended
Each series of Line of Duty brings huge drama and major twists – so it’s only right that there’s been a bit of down-time in the show’s world.
Series 4 picks up one year after Series 3 ended, and things are ticking along.
“Everyone is still in the same role,” Mercurio says. “Kate is now a Detective Sergeant having been promoted at the end of the previous series.”
3) Thandie Newton is the new antagonist
Line of Duty trades in shades of moral greys, but Newton’s character DCI Roz Huntley is the latest antagonist for AC-12 to face.
“She is a very intelligent and capable officer, a working mum with two kids, who took a career break of five years to look after her kids and as a result she’s not as far along in her career as she would have hoped,” Mercurio explains.
”She’s very ambitious and well educated, she really knows her job very well and she has a great deal of loyalty from her team and is well liked by her superiors.”
4) There’s another new cast member
Newton isn’t the only fresh face to join Series 4. Jason Watkins has been added to the show as forensics expert Tim Ifield.
“Tim’s a forensics expert, not only is he a very detailed and brilliant practitioner but he is meticulous and professional,” Watkins reveals.
“Often these guys can solve the case themselves and I think because they have the ability to do that, sometimes there’s friction between other departments.”
5) It’s easy to catch up
If you’ve not seen any Line of Duty so far, don’t worry – all three seasons are currently streaming on Netflix.
There’s also a 12-minute Series 1 and 2 catch-up on iPlayer for those wanting a super-snappy refresher, as well as the full third series.
6) There will be as many twists as ever
Above all, Line of Duty has become well-known for those brain-bending twists you never saw coming – and that’s not changing in Series 4.
“We hope once again to torment the nation with twists and turns,” Mercurio teases.
BBC One, 9pm, Sunday