Every novelist has a different relationship with his or her characters. David Mitchell's write him letters. "It's true," he says, rummaging for a notebook and flashing a double spread of intricate handwriting. "At the top here," he says, "we have things like 'Dear Dave', if they know me very well, and 'Dear David' if they're being more formal. Then they write about who they are, childhood experiences, first memories, what they think about other people in the narrative, what they think about God, money, work, sex, Conservative-Liberal politics, which newspaper they read. Their education, of course. The point about it being a letter rather than a biography is you're getting it in their own voice. You're in search of a voice." He thinks for a moment. "What they're afraid of is important. And what they want."
Both his breakout third novel Cloud Atlas (2004) and last year's The Bone Clocks were giant zones of experiment, splicing interlinked fictions into symphonic fantasies that contained multitudes and spanned centuries in time and literary genre.
The grand ambitions of Cloud Atlas attracted the grandiose ambitions of the Wachowskis, directors of The Matrix, who adapted it to film in 2012. Mitchell, who says it was a "very positive visit to the republic of film", has recently sold the rights to adapt The Bone Clocks as a television mini-series. In between those two landmarks, though, he also wrote a semi-autobiographical novel set in 1970s' Worcestershire and one set in 18th-century Japan - and now, in this year's short novel, Slade House, he's written a ghost story, or at least, as he puts it, "a compendium of ghost story outcomes".
It's a startling body of work to have emanated from one mind. I meet Mitchell, who is tall, lean, boyish, squeezed into a table in a hotel cafe in Cork, where he has lived since 2002 after stints in Italy, Japan and Britain. He has an air of such quiet rationality that one almost wants to question his credentials. You might peg him as the friendly sidekick, dispatched to give interviews while the real Mitchell sits raving about immortality and apocalypse.
The impression lasts about as long as it takes for him to open his mouth, or perhaps for me to ask him whether the rapid switches of perspective in his novels signal that he gets bored easily as a writer. "Oh God, no!" he says. "No, no, no. I can't imagine getting bored artistically. No. There are so many things to write! There's just the world!"
He continues: "Boredom's a kind of Geiger counter I have on me. The moment it starts to blip I know I'm going in the wrong direction. You can be pretty sure that if it bores you it's going to be boring a reader, and vice versa. No, no. I've got an argy-bargying shortlist of my five or six next books, they've formed an unruly queue and they're constantly trying to jump in front. It's not boredom that's my problem. It's the fact that these books are quite substantial and they need time. They need input. And to provide input I need to top up the reservoirs of raw material and research. And alter who I am in order to write them."
Slade House is a companion piece to its gigantic predecessor The Bone Clocks. "It's almost a dessert if you've read The Bone Clocks," he says, "and a starter if you haven't, and hopefully a standalone amuse-bouche if you're not going to, which is fine."
Told in five parts, by speakers who relate their stories in the present tense from "the foremost tachyon of the wave of time that's moving through the narrative", it revolves around a creepy mansion that appears every nine years behind a metal door on a London street. Without wishing to give too much away, readers of the previous novel - in which a clan of immortal consciousnesses known as the Horologists waged war across the centuries against the evil, soul-eating Anchorites - will find an unpleasantly familiar surprise waiting at the centre of Slade House's web.
Creating what he describes as a "traditional genre piece" seems to have amused Mitchell intensely, and he smiles when I mention the book's suspenseful focus on repetition, as character after hopeful character walks up the garden path to their dismal end.
"My hope is that it can be a device to generate expectations," he says. "Then, when you can feel the reader thinking, 'Oh, this is a bit like the last one, I know what's going to happen next', you can go - whoops ... you don't." He makes a swishing noise. "Gotcha!"
Talking to Mitchell, it turns out, can be as much of a heart-racing experience as reading his books. It can also be disconcerting for an interviewer, since once he's given his answer he's in the habit of bouncing the question back and listening attentively as I grope for something to offer in exchange. After the third such return of serve ("Are you a Whovian or a Trekkie?" - he prefers Doctor Who and would love to write for the series), I remember a piece of writing advice he once gave a fan during an online question-and-answer session. "A great hint," he suggested then, "is to never interrupt when someone else is talking, and to gently nudge them into talking about those things about themselves that are most different to you and most unique to them."
Mitchell smiles when I mention this. "Well," he says, "unless you want to write one or two books and then vanish into a cycle of diminishing returns, you need to think a bit like a journalist, and I suppose encourage people to trust you. People aren't fools, and they generally know when you're doing that, so you actually have to mean it. You need to view anybody and everybody as a potential protagonist, and it's your duty of care to your future novels to enrich them by listening to people.
"You have to be aware that it's a privilege, and you shouldn't misuse it. But the best character-builder is not description but voice - that's no great insight, it's borderline bleedin' obvious. So you also need to be a phrase nerd, a language magpie, to catch things that aren't in your active vocabulary and write them down quick and store them away. All those different ways of saying the same thing."
Slade House (Sceptre $29.99) is out now.