Unforgotten writer Chris Lang: how personal tragedy led to new ITV drama Dark Heart

This six-part ITV drama stars Tom Riley as Will Wagstaffe, a detective who deals in particularly grisly killings.

Think victims castrated and slaughtered, with their eyes gouged out of their sockets and replaced with testicles. Grim.

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As a teenager, Wagstaffe and his sister Juliette (Charlotte Riley) lost their parents to a still-unsolved double murder, a bereavement which has had a huge impact on the siblings' lives.

For Lang, there was a personal edge to this particular story. Eleven years ago, his wife Lydia died by suicide after a struggle with mental illness, leaving Lang a widower with three young sons.

It was in the aftermath of her death that he first encountered the character of DI Staffe in the Adam Creed novels, which serve as the inspiration for Dark Heart.

"At that time in my own life, I was wrestling with personal grief," he says. "My wife had just died. And his was about his parents, who'd died when he was a 15, 16 year old.

"And it was a lot about how that affects you," he continued. "Whether you can ever move on from such profound events. I was struggling with a lot of the same issues myself. So I thought I could write about that from a very personal perspective."

Was it painful? "Very. Yeah. Always. I mean, all of your life's experience comes into your writing: this show has a lot about mental illness in it, which is what I was dealing with at the time," he says. "Not myself, but my wife's, and so yes I understood that, I understand it, and yes it's painful but it's necessary to express it, to expunge it, to get it out there.

"Not everything I write is personal by any means. But certainly in the second series of Unforgotten, there was a huge amount of my own experience in that. And if you write from a personal experience I think the audience can sense it and they feel the truth of it, and they feel they know that they're talking to someone who understands a subject."

To write a series like Dark Heart, Lang has to access his own pain and memories of grief and loss: "If you watched me in my office, you'd see me typing – and I'd be crying quite often."

However, the experience also proved to be cathartic.

"You begin to understand what you think about something when you start to express it," he explains. "Either by talking about it, or in my case by writing about it."

"So I would say it helped shape me, some thoughts in my head, and helped me find my way through certain things," he adds.

Since the loss of his wife 11 years ago, Lang has remarried. His second wife Frances Lang is CEO of children's charity Variety, and between them they have five children who clearly fill him with a huge amount of pride.

Perhaps that's why, across all his dramas from the last few years, he traces one core theme: "They generally tend to be about family, and how strong or not family can be when presented with various difficulties and vicissitudes."

Lang and his family now live in London, and Dark Heart has given him the perfect chance to set a series in the city he loves.

"I've lived in London most of my life and I've always been fascinated by the old parts of London and spent many, many weekends wandering around there.

"I love the duality of the modernity and the ancient, and I love the fact that London is still built largely on the footprint of the medieval city and you can see all of that, a thousand years of history right next to the latest Gherkin or Shard or whatever.

"And I thought that was a really interesting metaphor for the timeless nature of the battle between good and evil."

If Dark Heart is sounding familiar, that's because the first two episodes have already aired in a different form – playing out as a feature-length TV movie on ITV Encore, the short-lived ITV channel on Sky.

Encore has since been closed down, but Lang's drama has been given a new lease of life on the main ITV channel with six episodes and a primetime slot.

"Where did it go? What was it? What was it in the first place?" Lang jokes, of the ill-fated Encore. But, he, says, "in a way it was a great place to pilot something, because you have a lot of freedom and it wasn't perhaps under the constraints of a classic nine o'clock primetime show; we could be a bit more experimental."

But now Dark Heart is actually set to become a 9pm drama, producers have given it a bit of a revamp. Lang describes it as "a slightly different animal," one which holds back details of Staffe's parents' murder until later in the series – and removes a memorably stomach-churning shot from episode one.

"There is one explicit shot that we've had to remove," he says, describing the scene: "Testicles for eyeballs, yes, testicles for eyeballs. I mean, the action will still happen, we just won't actually see it.

"Because actually although it is gruesome and dark and violent, actually it's not particularly explicit apart from perhaps that scene. You don't see it. I'd say 99 percent of it is suggested and lets the audience do the rest with their imagination. Which is how I always like to write stuff anyway."

The drama follows Wagstaffe as he investigates these brutal murders while attempting to hold his fractured life together.

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The two-part stories air across consecutive nights (Wednesdays and Thursdays). Episodes one and two are about a string of vigilante attacks on alleged paedophiles; episodes three and four look at underground organ harvesting; episodes five and six focus on murders in the world of pornography.

But the core narrative arc reveals how Wagstaffe's bereavement continues to impact both his work and his personal life, affecting his on-off relationship with girlfriend Sylvie and his bond with sister Juliette.

Echoing the drama's title, Lang says, "It is dark, but it has tremendous heart, I hope."

Dark Heart airs on Wednesdays and Thursdays at 9pm on ITV

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