IN a douce, respectable house on Glasgow's south side, a man and a woman are coolly, calmly talking about murder.

They are not husband and wife. The woman's husband is not at home. He's gone off to the post office leaving the woman - let's call her Helen - and the other man - shall we say, Doug? - to talk about how easy it would be to kill; how simple to end someone's life, or change it forever.

"I spent a morning looking at images head wounds just to get it right," the man says, "and then thought, 'What have I even been doing the last few hours?'"

"You'll have a day when you think, 'The things I've Googled today!'" the woman agrees.

There's fresh coffee in the cup, family pictures on the fridge. This is a home. But sometimes home is where the hurt is. This man and this woman know that all too well. They make a living from it.

For some years now Doug Johnstone and Helen Fitzgerald - whose home this is and whose husband, screenwriter Sergio Casci, has popped out - have been making a living from writing about death in places such as this. They are proof that the domestic noir - to give it a label - did not begin with Gone Girl.

In this they have also been reminding us what we all know deep in our hearts. Murderers, and their victims, are always somebody's son or daughter.

Still, things have changed since 2012. We are in a new era, the post Gone Girl era. Gillian Flynn's novel has been a phenomenon. The book has sold millions, is now reportedly the 25th best-selling adult fiction title of all time, has been made into a hugely successful movie and prompted publishers to scramble around for Gone Girl type books - thrillers that explore themes of marital break-ups, domestic violence, mental illness and murder. Always murder.

Fitzgerald and Johnstone are two of Scotland's best practitioners of the form. Read through their back catalogue and you'll find stories about a missing wife and mother (Johnstone's Gone Again) and infant mortality and parental guilt (Fitzgerald's The Cry).

Their latest novels plough the same dark furrow. In her latest book, The Exit, Fitzgerald deals with dementia, terminal illness, the generation gap, and care, or the lack of it, in care homes, culminating in a disturbing climax.

Johnstone's next book, out later this year, will look at the subject of teenage suicide, while his latest in paperback, The Dead Beat, also explores mental illness, the generation gap and newspaper obituary pages and kicks off with its heroine Martha receiving a memorable phone call. "I read about someone who committed suicide when on the phone to someone else and immediately my reaction was - what would it be like to be on the other end of that phone call?" he explains.

There are no Rebuses or Scarpettas here. No flawed police heroes. No forensic scientists finding clues in blood spatter patterns. Fitzgerald and Johnstone's books are concerned with amateurs, not professionals. Their protagonists could be me or you, family members who suddenly find themselves at the heart of a crime. The question they face is how they deal with it.

"What could be more dramatic than if you're personally, emotionally involved in the crime?" explains Johnstone. "If you've committed the crime, or your brother or daughter or mother or son have committed the crime and you know about it, that's surely going to have more of an emotional impact with the reader than Detective Inspector Doodah who's got his own problems in his own life."

"Why would you write about the onlooker in an interesting situation?" agrees Fitzgerald. "Why wouldn't you get right into the middle of it? I am nosey and I'm interested in other people's crises and I believe ordinary people do bad things. I don't believe in evil. Everyone is capable of doing bad stuff. That's why I do the job I do and write the books I write."

Why, you might ask, would you want to poke a stick into murky waters in the first place though? What draws them both to the dark? "Why?" Fitzgerald asks. "I think I'm f***** in the head. Happy stories are dull."

You could write a comedy. "Comedy's really hard. I got halfway through a screenplay and killed someone. It was a comedy up to that point."

It should be said that Fitzgerald and Johnstone are funny, in person and in print. Johnstone who's been a musician, a journalist and a nuclear physicist in his time, he is originally from Arbroath and now lives in Portobello with his wife and children. Fitzgerald, lean, sharp-featured and sharp-tongued - I can't even repeat her best lines because 1) it would be a spoiler and 2) that stuff about descended testicles might be too close to the bone - originally hails from Australia (her accent is still intact) but has settled in Glasgow. She is also a part-time social worker and so is well aware of how easily and how often domestic life can go awry.

The two of them are colleagues in their chosen profession, chatting about crime festivals and fellow writers in between talking about the meat and blood of what they do.

There is much to discuss. The success of Gone Girl has shivered through the publishing industry and the question is: why? Why did Gone Girl have the impact it did? And why are readers clamouring for similar fare?

One domestic noir thriller writer Rebecca Whitney - author of The Liar's Chair - recently suggested that in a time of geopolitical uncertainty, many people concentrate on the thing that they think they can control: their home environment. And that's exactly why the idea of things going wrong domestically carries such a charge.

Fitzgerald reckons there is something in that. "I hope people will feel upset reading my books and I think it's scarier for them to imagine the safest environment is the one where everything goes wrong.

"And actually," she adds, "it's more realistic. It happens more often than tornadoes."

"People are always having affairs and killing spouses," says Johnstone. "And that happens in the streets all around us as opposed to James Bond jumping off a plane onto a train or whatever crap he's up to now.

"You don't have to stretch the reader too far because everyone's got a domestic life."

And so everyone knows that domesticity is not always like a Persil ad or a Facebook update."You should never compare your own life to other people's as they present it on Facebook," Johnstone points out, "because that's a fantasy, a fiction."

Johnstone and Fitzgerald deal in what-ifs. What if, for example, a husband's wife failed to return home one night leaving him with a child to look after (as happens in Johnstone's Gone Again).

"That just came from when I was a house husband and my kids were younger and they were both acting up and I was having to get the tea made. I was pretty much at my wits' end and my wife commutes round the bypass and it was: 'What if she doesn't come home? What would happen then? What would I do?'"

For The Dead Beat, Johnstone drew on a passing comment by his sister-in-law, a nurse who once worked in the psychiatric ward in the maternity unit who suggested that in certain circumstances, electro-convulsive therapy can be helpful. "Everyone thinks it's a bad thing because you imagine One Flew Over The Cuckoo's Nest, which is a) fiction and b) 1973. It's not quite the same thing now."

How close is this material to their own lives? Sometimes in the same neighbourhood at the very least.

Johnstone himself thinks he suffered mild depression in the wake of an operation a few years back. "It was never diagnosed but in the recuperation period I was definitely clinically depressed. I never did anything about it and eventually it went away. I think it's incredibly common. I'm very wary of issue-y books and in The Dead Beat Martha has much bigger problems than I ever had, but in my family there's a history of depression. But then it's in everyone's family. One in four people have mental health issues."

Fitzgerald's latest book features someone dying of terminal illness. It's something that came out of her own life. A few months before she started writing The Exit she was caring for her dying father. "It is a strange way to put it but it was kind of life-saving for me. He was a great patient and it was a lovely thing to be able to do and I enjoyed it. I enjoyed the caring experience and I felt I improved as a person after it."

Was it difficult to then translate that experience into fiction? "No, that was the easy bit. That came naturally. If there's some form of emotional connection it's easier to write."

Even so, like every author there must be some form of self-policing involved in the writing process, especially when you stick so close to home for your themes. Sometimes too close, Fitzgerald admits. "The last book I started I wrote about 30 pages of a teenage suicide." Then she remembered that Johnstone was already working with that idea and equally as important, the subject was a little too close for comfort.

"I've got a teenage son and I just couldn't do it. It made me feel sick. Also, he overheard me talking about it and because he's a typical teenager he started thinking, 'Are you worried about me?' And so I thought, 'I'm not going to even go there.'"

There's something we haven't talked about yet. A question or maybe an assumption. The idea that domestic noir is in some way a feminine form. If the home is - even now - so often seen as a woman's space, is that also the case in domestic noir?

"There are definitely more women writing domestic noir than men," Fitzgerald admits. "Just the very word 'domestic' usually means a female protagonist. And there's maybe a little bit of sexism at work. It's the world.

"I write about women because it's what comes naturally. But I don't like books or films where it's all men and in the first 10 minutes you haven't seen a woman. It's really important to me that you have proper female characters. I'm not interested otherwise."

Rebecca Whitney has also suggested the number of domestic noir books - and their success - may itself represent a recognition of the fact that the victims of violence within the home are for the most part women. "Perhaps this new generation of authors," she wrote, "are vocalising a form of collective rage that not more is being done to understand and help women who suffer at the hands of an abuser."

Fitzgerald sees a truth in that. "I write a lot about domestic violence and abuse - sounds really cheery - and I work with sex offenders and it's 99% men that are the perpetrators."

Johnstone, though, in some ways gives the lie to this gendered definition. He has written in the voices of both men and women. In his books the thing that unites the sexes is their capacity to be wrong, to make mistakes, to screw up. Heroism is not the word that applies.

"Whenever I read a book or see a film where there's a big handsome hero banging women and solving crimes I'm not interested because it's just so archetypally stupid," he says ." I can't be bothered with it. It's not real and there's no emotional engagement."

There are no heroes. That's what domestic noir tells us. There are just flawed men and women.

"If we were in [the TV series] Lost I don't imagine myself as a hero, do you?" asks Johnstone. "I'd be the duplicitous snake. I'd be scheming. If there were two rival gangs I'd be in with them both."

"In reality that's probably who I'd be too," says Fitzgerald, "but I like to think I'd be the person who would work out how to light a fire."

The Exit by Helen Fitzgerald, in shops on February 5, and The Dead Beat by Doug Johnstone, which is out now, are both published by Faber, £7.99