Unforgotten writer Chris Lang reveals plans for "one more series" of the ITV crime drama

"I hope not, I hope not," laughs writer Chris Lang. "I’d love to come back for another go, I’d like to do one more series, because I want to square various circles with Cassie and Sunny."

"And I’ve certainly got another story to tell but it will be down to the audience and the broadcaster, whether they want it to come back," he tells RadioTimes.com.

ITV isn't in a position to confirm whether or not that third series will come right now - it's all still in the hands of the commissioning gods.

But Unforgotten has been something of a sleeper hit since it debuted on ITV in 2015, with Walker and Sanjeev Bhaskar teaming up to solve the historical murder of a child. The series was very well received by audiences and critics alike, and Tom Courtenay picked up a Best Supporting Actor BAFTA for his role in the first six episodes.

Unforgotten writer Chris Lang

The second series was hotly anticipated and wiped the slate clean, with what appeared to be a straight forward decomposing body in a bag murder case. But by the end of episode five, a much more sinister tale of child sex abuse and multiple murders had emerged.

Cassie and Sunny unearthed a plot hatched by three victims of child sex abuse – Sara, Colin and Marion – who conspired to murder each other's abusers in the early 1990s. Series two's victim, David Walker, was just one of the targets.

And when Cassie finally caught the 'culprits' – who had claimed to have no knowledge of the victim or each other – meeting together in a pub, she was forced to decide whether or not pursuing them for multiple murder was the right course of action to take.

"It was always going to be the theme," says Lang of the series two plot. "I knew right from the beginning what I wanted to say and in many ways I feel I achieved more in this show in terms of it being the show I wanted it to be than in series one."

"The idea for Unforgotten as a series came from the Stuart Hall case and then, for a number of reasons, I didn’t want to tackle sexual abuse in the first series," Lang continues.

"We came to writing this series at about the same time as there were some rather brilliant documentaries being made about some of the recent historic cases and some of the people who had been the victims of historic sexual abuse.

"I was reading a lot about it and I also had personal experience of sexual abuse through friends and various family members. I knew a lot about it and what I wanted to write about, right form the beginning, which absolutely fitted into the structure of Unforgotten, is the sense of child sex abuse being something that destroys whole lives."

Lang says that he felt the structure of Unforgotten – a show that allows a story to span decades – was the ideal canvas upon which to portray the infinite impact of such a devastating experience.

Actors Mark Bonnar and Rosie Cavaliero were charged with delivering powerful monologues about the abuse their characters suffered and Lang admits that he still feels incredibly moved watching them back.

Mark Bonnar as Colin Osbourne

"I know Andy the director was referencing various documentaries, he kept it very simple, there were no tricks there. It was just really talking heads. I think we both watched the documentary on the Saville case where they just talked to a number of his victims and they were talking heads. That’s all they were, there was no jiggery pokery in terms of the camera work because really you just wanted to see the peoples’ faces and hear their stories," he explains.

"It doesn’t fail to move me, no matter how many times I see it. [Unforgotten] is fiction, but I know people that this has happened to."

What does he hope real-life victims of abuse take from the series, then?

"That people understand them, I guess, that people understand the difficulties they go through and how that might manifest itself in the way they live their lives. That’s all you can hope for," he says, adding that the show doesn't offer any trite answers.

"[Child sex abuse] is appalling and you want to really tell a story that reflects that. It’s bleak and it’s hard and I think that’s the reality."

Rosie Cavaliero as Marion Kelsey

It's not entirely clear what happens to Sara, Colin and Marion, the accused trio, at the end of series two, so is there a chance they could play a part in Lang's dream third series?

"No, I think their story has ended," he clarifies.

"The audience will wonder which of those relationships survived and which didn’t. It’s quite a thing to learn from your partner that, albeit thirty years ago, you murdered someone. You might say that there were justifiable reasons but it’s still a heinous crime. What would you do if you found out? If your husband had killed somebody thirty years ago would you still be able to carry on your relationship with them?"

But for Cassie and Sunny the story is anything but over in Lang's eyes – and their decision to walk away from the case is one that he promises will hang over them.

"I don’t think it’s something that they will wear lightly. I hope the audience sort of feel that that was a very difficult decision to make. You can argue whether it’s the right or the wrong one, but it’s certainly one that I think you can understand given what those characters had been through," explains Lang.

"It’s a secret that they now have and they will have to carry with them through their job and if we do get a third series obviously one will attempt to explore the ramifications of what making such a profound decision will be."