Martin Compston: 'Line of Duty' fans 'will need therapy' after next episode

Mother of God - Line of Duty’s Martin Compston says viewers “will need therapy” by the end of the next episode of the hit BBC drama.

Compston, 36, who plays DI Steve Arnott in the hit crime series, shared a sneak peek at the next episode on Instagram today, with the caption: “Episode 5 kicks off as stores re-open and there’s a sale on waistcoats.

"In all seriousness though if you thought Ep 4 ended on a cliffhanger, you’ll need therapy by the end of Ep 5."

This comment comes as viewers were pausing the show and squinting at their TV screens to try and figure out who DCI Joanne Davidson — played by Kelly MacDonald — is secretly related to in the force, after Arnott revealed a DNA match.

Watch: A teaser for Line of Duty S6

Read: Line of Duty: Who is Jo Davidson's mystery relative? All the best theories

At the very end of the latest episode, Arnott revealed the news to Superintendent Ted Hastings, played by Adrian Dunbar, handing him a document featuring the details of the individual saying: "He’s identified over the page.” This gender detail was quickly pointed out by viewers.

So shocked by the DNA revelation, Hastings let out an infamous “Mother of God!”

The cliff hanger has fuelled speculation by fans on social media of who the relative may be, but it is unclear whether the individual is a new character or a character from a previous series, with many fans speculating the latter.

One viewer commented on Compston’s Instagram post: “I’ll definitely need therapy. Been an anxious mess since Sunday’s episode.”

Another poked fun at the actor’s mid sprint stance saying: “Mind that back!”

Read more: Line of Duty series 6 episode 4 recap

This is a reference to Arnott’s debilitating back injury sustained in a previous series, which has led to a medication dependency. We also saw him looking anxious as he was called in for a routine drugs test after John Corbett's wife Steph — who Arnott spent the night with — tipped off Hastings.

In the previous episode, Arnott was seen grimacing as the convoy van he was in with Jimmy Lakewell, the OCG (organised crime group)-linked lawyer from series four, who he had just removed from prison, was intercepted and overturned leading him to land on his back as he shot an attacker in the window above.

Watch: Denise Van Outen and Eddie Boxshall spice up their relationship during cooking therapy