Here’s the lowdown on what to expect from the return of Line of Duty – TV’s twistiest thriller which will be back on our screens on March 26.

Get ready to perch on the edge of your sofa and bite your nails to the quick once more as super-tense thriller Line of Duty makes its return to our screens. To get you in the mood, here’s everything you need to know…

Line of Duty

There’s tension in AC-12

It’s business as usual for the stalwart trio of Superintendent Ted Hastings (Adrian Dunbar), DS Steve Arnott (Martin Compston) and the newly-promoted DS Kate Fleming (Vicky McClure), as they try to sift out more police corruption. PC Maneet Bindra (Maya Sondhi) is also on hand once more to help crack their latest case, while Murdered by My Boyfriend’s Royce Pierreson joins the team as DC Jamie Desford. But there’s friction between Kate and Steve…

“You see how things play out after Kate’s promotion,” says Vicky. “There is competition with Steve. They are supportive of each other but also fiercely ambitious.”

Line of Duty Thandie

Thandie Newton is under suspicion

After Keeley Hawes, Lennie James and Daniel Mays played AC-12’s adversaries, now Hollywood star Thandie Newton is arousing their suspicions. The Westworld actress plays DCI Roz Huntley, who has been the senior investigating officer in charge of a high-profile case known as Operation Trapdoor. But when doubt is cast over her handling of the case, she comes onto the anti-corruption squad’s radar…

“She is under a lot of pressure but the audience will have to be the judge and jury,” teases Thandie. “My agent told me that if I wanted to work in British TV, Line of Duty was the best thing I could do. So I caught up with the third series and it was phenomenal.”

Jason Watkins

Jason Watkins (above)

Lee Ingleby

Lee Ingleby

Meet the new boys on the block

Thandie is not the only big guest star this time around. Trollied and W1A star Jason Watkins plays geeky forensic co-ordinator Tim Ifield who clashes with Roz over her case. Meanwhile George Gently and The A Word star Lee Ingleby plays Nick Huntley, the husband of mother-of-two Roz.

Line of Duty

The interrogation scenes are just as long and tense

The series has become famous for its nail-biting interrogation scenes as AC-12 questions its prime suspects and witnesses, and this time around there’s still no let up. “I call the show Lines of Duty,” laughs Vicky.

“Those scenes are like theatre,” adds Thandie. “I had one that was 25-pages long! I got my kids’ nanny to test me on my lines. She would dread it – I should have paid her a bit more!”

Jed Mercurio

The series has been promoted to BBC1

After three series on BBC2, in a sign of its ever-growing appeal, the new series will air on BBC1, while writer Jed Mercurio is already writing a fifth run.

“The BBC felt that it had done well on BBC2 and asked if we fancied a transfer and we were very grateful for the opportunity,” says Jed. “We felt we had reached the conclusion of a lot of storylines with the end of series three so we approached this with the view of starting a new chapter.”

Here’s a trailer from the new series

Line of Duty returns on Sunday March 26 on  BBC1