The Good Nurse writer reveals detail she couldn’t include in film

Wilson-Cairns was working on the script for a number of years before the film was made, adapting it from the non-fiction book of the same name by Charles Graeber, and naturally, she was unable to fit every aspect of the case into the screenplay.

"I mean, there was so much," she told RadioTimes.com when asked which parts of Graeber's book had to be left out.

"You know, we were telling the story from Amy's point of view, so we never really could go outwith it – but the way in which Charles Cullen was passed from hospital to hospital, the way in which he was dismissed for stealing supplies like toilet paper, or he was dismissed for putting the wrong dates on his application form.

"And every single one of these hospitals – or at least, the people within these hospitals – strongly suspected that he was murdering patients, and not just one or two, murdering multiple patients. And I just think that to me is such a failing of everything – of humanity, of the system, of law enforcement procedures.

"And that was so galling. And, you know, there are obviously parts of that in there, but we couldn't put that in."

Wilson-Cairns added that when she first read the book she initially had no idea how to tell the story as a film – and it wasn't until Amy Loughren appeared in the final third that she realised what her focus should be.

"The first half of the book, I was like, it's so compelling and so fascinating, but I'm not sure the way in – I don't know what the emotional core of the story is," she said. "I didn't want the serial killer to be the lead, like I didn't want him to be the star. So I was really, really struggling with it.

"And then in the last third of the book, you hit Amy Loughren and her story. And I thought, OK, well here's a working-class single mum, a working nurse who is oppressed by the system and is also having problems because of her health and the way healthcare is set up in America.

"She was closest with the patients, she was also closest with the serial killer. And I thought, that's your way in because that's actually the human element of the story, she was the humanity in all this darkness for me.

"And also the fact that she doesn't defeat him with violence, she doesn't bully him into a confession. It's not like she shoots him or something like that – there's none of these traditional narratives of how you kill the villain. She overcomes him with compassion."

As part of the process, Wilson-Cairns met many of those involved in the story – including Amy Loughren – and she said this was an "integral" part of the adaptation, adding that Loughren was "so gracious and open".

"It's one thing to read that a person has a heart condition, but it's another thing to hear in their own words," she explained. "Like, what does it feel like? Oh, it feels like your heart's trying to burst out through a vein in your neck.

"And having an understanding of that when you're writing it then has a knock-on effect – I know that Jessica Chastain worked together [with Amy] to really understand that heart condition as well. And then the other thing, which I found out was that she actually had collapsed on shift with Charles Cullen, so that's all true."

Read more: The Good Nurse writer on “truly terrifying” Eddie Redmayne scene

The Good Nurse is showing in select cinemas now and will be available to watch on Netflix on 26th October. Sign up for Netflix from £6.99 a month. Netflix is also available on Sky Glass and Virgin Media Stream.

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