Mark Haddon: This year's big read

A 'difficult' novel whose teenage narrator is incapable of expressing emotion is already being hailed as a literary classic to rank with the greats - and will be seen on every Mediterranean beach towel this summer. John Walsh explains how the uniquely beguiling Curious Incident of the Dog in the Night-time struck publishing gold

Next Tuesday evening, at the head offices of the Whitbread brewery in the City of London, amid the glammed-up writers, publishers, literary journalists, television celebrities and media horizontales of the metropolis, among the picturesque dray-horses in the company's front yard and the camera crews in the main dining hall, in all the howling paraphernalia attending on the Whitbread Book of the Year award, the focus of attention will fall on a 15-year-old boy.

The kid will not be there in person, because he's a fictional character, the narrator of Mark Haddon's much-admired, bestselling novel The Curious Incident of the Dog in the Night-Time - but if he were, he would a) absolutely hate it, and b) have no clue what was going on. Because Christopher Boone doesn't understand why people do things. He suffers (though the book never actually tells you) from a form of autism called Asperger's syndrome. He can't understand the motivation behind actions or the reasons for everyday human behaviour. He can feel pleasure and contentment, sadness and fear, but can't intuit or grasp the emotional vocabulary of others. A mathematical genius, and a whizz at physics and cosmology, he lives in a world of facts and logic, in which people are scary and threatening because they tell jokes he can't understand, they use figurative language that makes no sense, and they're always trying to touch or embrace him.

He is by some distance the oddest and most original narrator to appear in years; indeed the book's appearance has created a stir comparable to the early days of JK Rowling. It has the quality of making everything around it seem a little muddy and indistinct. In the five categories from which the eventual Book of the Year will be drawn, Haddon's book won Best Novel, while the winner of the Booker Prize last October - DBC Pierre's Vernon God Little - had to be content with Best First Novel. The Curious Incident is, technically, Haddon's first novel for adults, but it was also published as a children's book (his 16th) and won the Guardian Children's Prize in November. Confused? Even if it doesn't win the overall prize on Tuesday and is pipped by DJ Taylor's biography of Orwell or Don Paterson's poetry collection Landing Light, it will still be the season's most talked-about book and the strangest bestseller to hit the nation's shelves since Flaubert's Parrot.

Since publication in June, Jonathan Cape has shifted 150,000 copies in hardback, and sold the rights to 40 countries. Sales in Italy, for some reason, almost match those in the UK. It's been praised by reviewers across the spectrum, by Ian McEwan, doyen of the novel of ideas, and Oliver Sacks, the presiding genius of neurological drama, and chosen as Book of the Year by such literary stars as Anne Tyler and Peter Carey. It has the potential to become a world-seller, with a paperback print run of half-a-million copies - the kind of book that shows up on the top deck of every bus in Britain and every beach towel in the Mediterranean - and becomes a "classic" in 20 years' time.

But why? It's no Birdsong or Captain Corelli's Mandolin. It eschews the standard attractions of the bestseller. There's no sweeping narrative, no backdrop of war, no international canvas. It's set in the suburbs of Swindon. There's no transporting love story (there's the fag-end of an infidelity-and-wife-swap story, but that hardly compensates). There's a murder mystery (Christopher tries to find out who killed Wellington, the neighbour's poodle), but it's solved halfway through. There's no character with whom to "identify" apart from the autistic narrator who, it's safe to say, couldn't possibly identify with you. The story is without stylistic flourishes. Because Christopher can only tell an unvarnished story, most of the paragraphs - and hundreds of sentences - begin with "And". Mathematical formulae, diagrams and grids chequer the pages...

Just to make things slightly more puzzling, the book was published by two different houses under the Random House umbrella - by Jonathan Cape (for adults) and David Fickling (for children) - each of which deployed its own sales force for a two-pronged attack on the bookselling trade. Amazingly, it seems to have generated a publishing phenomenon.

"The ground for its success was laid with JK Rowling and Philip Pullman," says Nicholas Clee, editor of The Bookseller. "No one in publishing will let the over-used word 'crossover' pass their lips anymore, but there are books that clearly appeal to adult and child readers, and can be sold to them in ways that weren't possible before Harry Potter came along. If it had come out 10 years ago, it would have been much harder to market to the book trade, and harder to persuade reviewers to take it seriously. Publishers would have been confused about how to categorise it, booksellers wouldn't have known where to stock it. Now if you say, 'It's a children's book that appeals to adults', everyone knows what that means."

"I read it in proof before I knew anything about it," says Sue Baker, books editor of Publishing News. "I knew it had got it - that magic ingredient. It's a perfect book, completely of itself; it doesn't have to be like anything else. It puts you so strongly in the mind of this kid that you know just what it's like to be him. It's probably a classic to be passed on to the children of the next generation."

To meet the author is to meet a very happy, slightly dazed man at his small, comfortable house in Oxford, among the rat-run of student dwellings between the Cowley and Iffley Roads. Mark Haddon is 40, stocky and boyish, in his sloppy blue jumper, green cords, Caterpillar boots and shocking pink socks. He makes real coffee with studied vagueness ("I never know how much to put in"), while his wife Sarah (known all her life as "Sos", and now lecturer in English at Brasenose College) bustles about with the tiny new arrival, Zac. It's a jolly household, bursting with colour and creativity. A vase of red and orange tulips explodes over the coffee table. In the grate, a long tube of winking lights substitutes for a fire. Haddon has had a number of careers - artist, cartoonist, poet, illustrator - and talks as energetically about his favourite artists as he does about his literary ambitions.

"When I first started this book, I thought, 'Oh look - it has layers'," he says. "It helps you get immediately into the mind of someone who would be totally closed from you in real life. It's a fiction about someone who says they can only tell the truth, but actually he gets everything wrong. He's a guy who should be a really bad narrator because he takes everything literally, who doesn't understand emotion and misses the big picture. But he turns out to be a really good narrator because he leaves a lot of space for you to add your own stuff to the story."

Haddon is a serious literary cove with a liking for the cutting edge. While little contemporary fiction gets him excited, "I feel like I'm out there on the runway in the dark, waiting for the Big One to come in, thinking, 'Maybe this is it'. I'm the sort of person who gets excited when someone like David Eggers comes along. I've always really liked experimental writing."

Had he started writing with big ambitions? "I've always had those. I've written great baggy monsters of purple prose - lots of high-concept stuff. One book was called The Blue Guitar Murders, about which I remember very little except that it involved the Via Negativa and a singing policeman. It should be published as a stern warning to over-intellectual 21-year-olds who want to write a big book. But you learn to throw all that out and I think writing children's books helped in that process because you can't indulge yourself when writing those."

So did he write The Curious Incident for kids? "No, I wrote it for me. I thought, there are no rules this time. I don't have to take into account who's going to read it, I'm writing for myself. I'm really glad that David Fickling [the children's book publisher] wanted to do it as well as Cape, and that teenagers are reading it." What response has he had from younger readers? "Very pleasing. Although there are a few prudish reactions from well-brought-up 13-year- olds, warning others that there's bad language..." Indeed there is. Most of the grown- ups in Christopher's life seem to talk in a blizzard of effing and blinding. "Do you think there's too much swearing?" asks Haddon in mock alarm. "Don't grown-ups swear a lot? We just don't notice it. I hear swearing a lot during the day, although admittedly it's usually from myself..."

I point out that his Radio 4 play, Coming Down the Mountain, broadcast last year, gave a voice to a Down's syndrome teenager called Ben. Was Haddon trying to corner the market in mentally skewed ways of seeing the world? "Am I going for the Disability Boxed Set?" he asks, laughing. "The answer is, you always want to get people in extreme situations because it shows who they are. You can't get through a novel on tea parties. You've got to have people in the burning building or the lifeboat. I wanted to be contemporary and ordinary, but have an edge. And this book - Christopher's adventure - does that." His experience of physical and mental handicap came in the early 1980s, when, just out of Merton College, Oxford, with an English degree, he worked for Community Service Volunteers in Scotland, looking after a patient with multiple sclerosis. "I worked in 24-hour shifts, doing everything for him - washing, toileting, smoking - and it was very black and very funny. It displayed the truth that, if you're sharing a house with someone who's paralysed from the neck down, it's often the person they're living with, the one with all his faculties, who really needs looking after. The guy we were supposed to be looking after, 99 per cent of his problems were about religion, sex and having rows with neighbours - the usual things. He had a serious disability, but it didn't define his whole life."

Moving to London, he continued his saintly progress working for Mencap and a Children's Action Workshop in Muswell Hill ("Everyone says, 'What's with all the caring?', but at the time it seemed very normal. We were quite a political generation"). "It was full of kids of all ages, with various physical handicaps and learning difficulties, some with mental handicaps. But there were no labels. When you went in there, you had to work out, 'Am I talking to a very articulate seven-year- old, or to a 12-year-old with growth and developmental delay?' That was a real eye-opener."

When did he first find evidence of the alien landscape that's inside his narrator Christopher's head? "Oh, I think that if you're a writer you have that in your own head from quite an early age. I think it's true there are two types of kids as school. One type probably breezes through school like gazelles across the veldt. For the more troubled types on the edge of the playground, how you get from one day to the next is a mystery. All writers come from the latter, because only if you're in that group does the working of the human mind become an object of interest."

At Uppingham School ("which produced John Schlesinger, Boris Karloff and, briefly, Stephen Fry before he ran away"), Haddon was himself a bit of a Christopher Boone about maths. "I'm periodically obsessed with the subject. And if you are, and you write novels, believe me, it's not that easy to drag it in." We talk about madness and eccentricity, how supposedly close to madness are some forms of artistic endeavour - and how autism is considered very much a male complaint (for some women, it's practically a definition of maleness). "The ratio of men-to-women Asperger's sufferers is nine to one. And we all know some middle-aged men with undiagnosed Asperger's. Go to a maths department in a university town and the ratio goes up sharply. A friend said: 'This not a book about Asperger's; it's about a young mathematician with behavioural issues. If Christopher was real, he'd go on to have a perfectly adequate place in any maths department, and be surrounded by people not very different from himself.'"

The news that film rights to this wholly unfilmable book have been bought by Warner Brothers, in cahoots with Heyday (the producers of the Harry Potter movies) and Plan B (Brad Pitt's production company) gives a pleasing arc to the phenomenon, which began quietly in June last year; grew through public disputation when John Carey, the chair of the Booker judges, publicly regretted his fellow judges' failure to share his enthusiasm for this "masterly and amazing book"; picked up the Guardian Children's Fiction Prize and the Book Trust teenage fiction award; hit the top of the bestseller lists twice; and began the new year by winning the Whitbread Novel prize. If Haddon walks off with the Book of the Year award on Tuesday, no one will be very surprised. Though they may find it hard to say why it has done so well.

"When I read it, I didn't think it was a kids' book anyway," says Nicholas Clee. "But it was a book I could confidently recommend to a lot of people, knowing that 90 per cent of them would like it - and you can't say that about many books now."

Blake Morrison, who also chose it as one of his books of the year, says: "I suppose if I were a Booker prize judge, I might be concerned with questions about its 'seriousness' or its 'major' status. But it was the thing I most enjoyed reading last year, and I'd recommend it on the pleasure principle."

Perhaps the reason for its success lies in a subtle trade-off between high seriousness and teenage playfulness. The Curious Incident of the Dog in the Night-Time is, in fact, a dazzling work of post-modernism. It has an unstable narrator, a plot full of holes and a whole smorgasbord of metafictional devices. It turns its back on the conventions of the classic novel as Henry James would have conceived it, with its subtly calibrated emotional shifts. Instead, it asks the reader to supply what Christopher's narrative is missing, and then to marvel at the pathos of his foreshortened world-view. And behind this clever structure, it tells a gripping story of a dysfunctional family, and a fractured consciousness going out to confront the world for the first time. Every reader has, I suspect, been responding to both his Inner Child, his Inner Nice Guy and his Inner Smart-Alec, all at the same time.