What horrifies horror writers?

For Swedish writer John Ajvide Lindqvist, it was the moment his only son disappeared in the woods when he was five.

"I thought he was gone forever, that I hadn't deserved him and now he had been taken from me," says the 48-year-old in an e-mail interview. "(It was) terrible."

His son, now 20, was eventually found, but it remains the most terrifying thing that has happened to Lindqvist, who used it as a starting point to write his 2008 novel Harbour, in which a six-year-old girl vanishes.

Lindqvist is the author of seven novels, most of them horror, but it was the 2008 film adaptation of his debut work, Let The Right One In (2004), that propelled him into the international spotlight and earned him the moniker of the "Swedish Stephen King".

Set in a 1980s Stockholm suburb, the book centres on 12-year-old Oskar, an introverted, bullied boy who befriends his neighbour Eli, a child who is in fact an ancient vampire that relies on murders to survive.

The film, directed by Tomas Alfredson, is critically acclaimed.

Lindqvist has recently finished a trilogy, the first of which was published in an English translation in September as I Am Behind You, a title clearly meant to spook.

In it, the inhabitants of four camper-vans awake to find themselves transported overnight from their campsite to an endless grassy field under a bright, sunless sky.

"In Sweden, we have a thing called Caravan Clubs," says Lindqvist. "A group of people that meets in different places with their caravans. A sort of moveable village, if you like. I knew that a group like that would be transported to a different place."

There is no clear explanation for the strange field, the sheer emptiness of which represents lack, says Lindqvist.

"The idea was to explore who we are when we have none of the things that normally create our identities."

It soon becomes clear that something is terribly wrong. The grass drinks blood. One of the children in the group, a six-year-old girl, is behaving in an uncanny, sinister fashion.

"(Children) are supposed to be innocent and mean no harm," says Lindqvist. "That only makes it so much easier for them to get to us."

Attempts by the group to leave the field only result in strange encounters - white figures with no faces, for instance - that represent their deepest fears.

What would the apparitions manifest as for Lindqvist? "Stockbrokers," he says. "Life coaches and personal trainers."

The book's original Swedish title, Himmelstrand, is less overtly terrifying, referring to popular 1960s Swedish lyricist Peter Himmelstrand, whose songs are the only thing that can be heard on the radio in the field. "The music hints at all the things that this place is not," says Lindqvist cryptically.

Himmelstrand translates from the Swedish as "heaven shore" - a hint, perhaps, at the purgatorial nature of the place the campers find themselves stranded in.

Lindqvist says the nature of the place will be further explored in the next two books in the trilogy, which have yet to be translated into English. The third came out in Sweden earlier this year.

The second part of the trilogy features a young aspiring magician called John Lindqvist.

It is quite autobiographical, says the author, who was a magician and stand-up comedian for 12 years and started writing in order to have things to say while performing his magic tricks.

Seven years after Let The Right One In was remade into Hollywood film Let Me In starring Kodi Smit-McPhee and Chloe Grace Moretz, Lindqvist's work continues to make the jump to the silver screen.

Border, a short story from his 2011 collection Let The Old Dreams Die, is currently being made into a feature film in Sweden.

However, a TNT television adaptation of Let The Right One In, which would have been set in Vermont and produced by Teen Wolf creator Jeff Davis, was dropped earlier this year.

Lindqvist is, in fact, relieved.

"I hated the idea from the beginning," he says. "But there was nothing I could do, due to contract reasons."

He does, however, recommend the "excellent" stage play based on the novel, which was first put on in 2013 by the National Theatre of Scotland and has since played around the world in countries such as South Korea and Japan.

He is now working on a collection of notes made while writing his previous novels, "a sort of look into the life of a writer - how it's done, and sometimes not done".

Quoting the Irish writer Samuel Beckett, he adds: "It will be called Fail Again, Fail Better."