Centring on Daniel, a young architect whose world is turned upside down when he is propelled into a similarly disturbing situation, Smith has deftly blended fact with fiction.
"The son character is nothing like me and the mum and dad are nothing like my parents, so they're all very much made up," he says. "All I had was the experience of sitting at my kitchen table and having two people I love tell me completely opposing things and not being able to decide what was true or not. I've also been to the farm where they live in Sweden many times so I know the landscape and all the people she was talking about very well.
"It was a very different story to what's in the book because the main character hasn't been there at all, and he doesn't really know anything about his parents."
Apart from his mother's illness, Smith has drawn on much of his own background. Like the author, Daniel has an English father and a Swedish mother, he is also gay - although unlike Smith he has yet to come out to his parents - and he also appears to live in the same south London flat in which we are sitting.
"One of the big questions with the book was, 'Is there any point in changing the shell of it?'," he explains. "There was no point changing the farm - because I knew the farm and that world very well - or in setting it somewhere like Manchester. It just felt very arbitrary otherwise, so I thought there was no need to change those facts and I like the feeling that those who read the book aren't quite sure what is real or not."
Indeed, the only significant difference lies in the self-involved Daniel's distant relationship with his mother.
"My mum and I have always known everything about each other so there weren't really any secrets," says Smith.
"That's not as interesting as somebody who has never really grown up because then you can structure the book as someone going on a journey from naivety to maturity. The intersection points became much more interesting because they didn't already know this stuff about each other."
As someone who has made a very successful living crafting exhilarating crime stories, Smith felt right at home when his mother's outlandish tales evoked the suspenseful atmosphere of a mystery novel.
"In terms of genre snobbery, thrillers are often accused of being detached from reality and of resembling a crossword puzzle, a Sudoku or a game," he says. "But that was my real experience of a person whose thoughts were completely consumed with the shape of a thriller, which is to say betrayal, mistrust, conspiracy and criminality. So when I was trying to recreate the feeling I had as a listener on that night, the shape of a thriller was the closest to that.
"If I had not used that structure, it would have lost much of the energy and tension of that night."
Having explored the clandestine world of 1950s' Soviet Russia in Child 44, Smith has now contributed to the burgeoning Nordic crime scene, in which novels such as Stieg Larsson's The Girl With The Dragon Tattoo and television shows like The Killing and The Bridge capture imaginations worldwide.
"I'm half Swedish and the book takes place in Sweden, so it's been folded into this literary world that's sprung up," he says.
"It's partly because there have been some great writers around who happened to have lived in Scandinavia, but it's also a world that lends itself to that particular kind of noir. In our brains, we all understand big cities like New York and London, where there's a huge diversity of people and various activities from the good to the bad, so that doesn't shock anyone. But when you look at pictures of this wonderful, open countryside and lovely farmhouses, there's this notion of a darkness underneath, which is a very powerful literary tradition.
"That image of the farm cuts both ways because, on one hand, it looks very beautiful, but on the other, there's nothing else around you for miles on end and the sun barely rises in winter, so it can be quite intense living there."
The Farm (Simon & Schuster $37) is out now.
