It will tell the true story of Delia Balmer (Martin), who survived a near-fatal relationship with serial killer John Sweeney (Evans). The four-part series is based on Delia Balmer’s memoir, Living with a Serial Killer, which writer Nick Stevens has adapted. As reported by the , the official synopsis for the four-parter reads: "In 1991, Delia leads an itinerant and solitary life in London working as an agency nurse.
When she meets fellow free-spirit John Sweeney in a local pub, it seems like the connection she has been searching for. "As the relationship develops, Sweeney's artistic, anti-establishment persona gives way to a darker side, culminating in a series of violent attacks on Delia, during which he tells her he killed his former girlfriend and disposed of her body in an Amsterdam canal." Discussing with ITV in a press pack for the series if she met with Delia before filming, Martin shared: "No, I’ve played quite a few real people and I have never met them before.
I don’t choose to do that, that’s how I work. "Our writer, Nick [Stevens], filmed a lot of footage of his meetings with Delia, which I had access to. I did meet her very briefly during filming, but only because she wanted to visit the set, and of course I was respectful of that.
" She continued: "I didn’t do lots of research into abusive relationships either, instead I just focused on the character, on who she was, how she responded to things, and what I could gauge about how she interacted with people.