Classroom superstar: American novelist Kim Edwards

Kim Edwards can't remember exactly how long her debut novel, The Memory Keeper's Daughter, has been on the New York Times bestseller list, poor thing. "Is it 48 weeks or 49? I do know it was 30 weeks at No 1." A remarkable achievement for a newcomer, by any measure, and since its recent UK publication straight into paperback, it has been climbing the charts rapidly here too.

American writers seem to combine literary finesse and page-turning readability more confidently than their British counterparts - think of two recent chart-busters, The Time Traveler's Wife and The Kite Runner - and US critics are less snobbish in their response. In this polished family drama, Edwards cuts right to the main event with true storyteller's instinct: a father's snap decision that will profoundly change all the characters' lives. One snowy night in small-town Kentucky in 1964, Dr David Henry delivers his wife Norah of twins, with only his nurse Caroline in attendance. The boy, Paul, arrives first, but by the time the girl, Phoebe, emerges, Norah has passed out. The doctor sees the signs of Down's syndrome in Phoebe's face and commands Caroline to convey the baby to an institution. The next day he informs his dazed wife that the little girl died. Later he shows her a grave.

The plot has two main threads: one tracks the destructive effects of the secret on the Henrys' marriage over 25 years; the other follows the story of Caroline, who disappears with Phoebe to Pittsburgh, where she brings up the little girl as her own.

All this poses a credibility problem. With such a structure, authors inevitably find themselves running along behind, constructing character, milieu and motive after the defining event. It's not so unbelievable that a Down's baby might have been sent to an institution in those days, but it's a mystery why David Henry lies to his beloved wife. Why did Edwards choose to structure the book like this? "I had never thought of doing it another way. I wrote the first chapter in a month and was very intrigued by the characters, who emerged fully formed. The event was like a stone dropped into the water creating ripples. Narrative action flowed from the characters' action."

Dr David Henry is possibly the most fascinating of her cast. He's an enigma who has covered the tracks of a humble and troubled upbringing, which included a sister with Down's syndrome who died. Now he walls himself up behind this new, terrible secret. "David is not an evil character, but a tragic one," says Edwards. "He needed control over his life. Confessing would shatter the world he knew." In fact the secret is not revealed to the family until after David's death - something of an dramatic anti-climax, but perhaps closer to life than some stagey death-bed confrontation. "I discovered the book as I discovered the characters. David simply ran out of time."

Creative writing coaching lurks everywhere in the contemporary American fiction industry. Look at the new Granta anthology, Best of Young American Novelists 2. All the 21 writers showcased have been on creative writing courses. Edwards, who is in her late forties, is not only a graduate of the Iowa Writers' Workshop, but now teaches creative writing at the University of Kentucky. As a student, "for me the most important thing was that I learned to read like a writer, to analyse structure and character on the page. But then I spent years as an apprentice." (Something many modern students are too impatient to do.) "I realised I was inexperienced and that writing might not bring in any money." Instead, she took a TEFL course and travelled for some years in south-east Asia with her husband, teaching and writing. "It was a very stimulating time. I had freedom, the chance to experiment in different genres." The whole experience bore fruit. Ten years ago her diverse collection of short stories, The Secrets of the Fire King, was published and named as a finalist for the PEN/Hemingway award.

"The idea for The Memory Keeper's Daughter was given to me by the pastor of the church I still attend. He told me of a man in his forties who had recently discovered he had had a Down's syndrome brother in an institution. I was drawn to the idea but also rather daunted, so didn't start writing it down for a while." In the end, "I wrote the first chapter then read everything I could, clinical discussions and the history of Down's, personal accounts about loved ones. Then I found a wonderful, generous community with whom I could sit down and talk." Phoebe, the daughter, is sympathetically drawn but Edwards did not try to get inside her head in the way she does with the twin brother Paul. "I didn't want to presume to speak in that voice." She is relieved at the positive reaction to the book from Down's experts and is "very humbled" to have been invited to speak at the next National Down's Syndrome Congress.

Following a group of characters across a long time span raises challenges. "It wasn't easy. The characters changed according to changing times." She's been interested that many younger readers haven't understood why Norah stays with her frustratingly secretive husband rather than leaving and making a life for herself. "Norah and her younger sister, Brie, were born on either side of a social upheaval" - the Second World War. "Norah defers to David as a husband and as a doctor." Brie, on the other hand, is a rebel. After Edwards had drafted the book, she took apart the four different points of view and considered each in sequence to see how it worked across the period.

What happens when your book goes mega? Edwards describes the American hardback publication by Viking as "quiet". The book was well reviewed, then picked up by the big chain booksellers Barnes & Noble for their Discovery Award, which guarantees front-table display. But even after that it continued to sell steadily in hardback and began to be discussed by reading groups, in the States as here a formidable buying force. The paperback launch was "not hugely bigger", but six weeks later the book hit the New York Times list. "It was really, truly word of mouth," she says. Here, interestingly, despite its literary credentials, Penguin UK have pitched the book to the mass market, with a quote by Jodi Picoult on the front cover.

What is it about The Memory Keeper's Daughter that appeals to a readership that apparently crosses gender, race and age? Edwards just laughs and says simply: "It would be wonderful to know." Reading groups she's addressed usually either talk endlessly about big decisions in their own lives, or about family secrets. She's clearly hit a nerve.

What next? The Secrets of the Fire King is being reissued with new stories included. Then Edwards plans to finish her next novel. She is superstitious about discussing work in progress. "I'd prefer not to talk about it yet; it would be tempting fate." She's taking two years off from teaching writing at Kentucky, where her aim with her own students is realistic: "Helping them to step to the next place from wherever they're at". What single piece of advice would she give to a tyro hoping to achieve what she has? "I learned in my early years that you have to write for the pleasure of writing itself. Forget the whole business of being published. First come to writing because you love it."

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