Eng Lit's leading expert on evil

Ian McEwan's new novel is about a budding novelist, basically a good child, who makes up a story that plays havoc with people's lives. The third McEwan to be short-listed for the Booker Prize, Atonement is a whodunit, a war story, a study of the English class system and a discussion about writing, but it also serves as a motif for its author's career, the story of a gentle man whose imagination regularly reduces his readers' minds to chaos. If you need to know what it feels like to want to rape your sister or to lose your three-year-old daughter in a supermarket, I can direct you to the relevant passage in his work. There was an inevitability about McEwan being the first novelist into print with a commentary on the World Trade Center bombing. He is Eng Lit's leading expert on evil.

"Although," he protests, "I'm not sure I believe in evil. I don't believe in God and I certainly don't believe in organising principles of badness."

But if we don't believe in evil, how do we explain these terrible things, I ask. "Well, you look at people and motives and genes and culture and nature," he says, surprised it needs spelling out.

We are at the kitchen table of his house in north Oxford overlooking an apple tree which has shed about a third of its cargo of knowledge on to his small lawn. It is not a rambling house like his old home in Oxford, which I visited when he was still married to Penny Allen, a journalist turned faith-healer turned vendetta-wager. Instead of a gazebo there is a garden shed. Such are the wages of divorce. But it is reassuringly domesticated. His 18-year-old son, William, now in his gap year, peels potatoes at the River Cafe (its proprietor, Ruthie Rogers, runs a kind of finishing school for scions of the literati), but McEwan still gets his younger son, Greg, off to school in the morning and cooks his supper. He calls Atonement his Jane Austen novel, and you feel even the most genteel of its characters would be comfortable taking tea here.

I remind him that telling stories about such people was not why he began writing. When he started, he once said, the prevailing authors - Angus Wilson, Iris Murdoch, Kingsley Amis - all seemed to come from a social milieu quite foreign to him: "I didn't know anything about the names of glasses and furniture."

Yet the plot of Atonement turns on a Meissen porcelain vase? "Well, I had to borrow a book on vases from James Fenton. What I know about vases is in Chapter One and Chapter Two of Atonement. But no, it's a good point. When I started writing, I could not have described the kinds of things that I've described in this novel and probably a lot of the efforts to be de-socialised and not rooted in any particular time or place in all those early stories actually came out of ignorance about the world. I was playing away from my ignorance, which is not quite the same as playing to my strengths. I had to go and find a strange new place of my own."

In this strange place you might bury your mother's corpse under concrete (The Cement Garden, 1978), pickle a foot-long penis (the screenplay Solid Geometry, which the BBC banned the next year), or hack a young man to death on a romantic holiday in Venice (the 1981 Booker-listed Comfort of Strangers). Exploring this locale, he developed a "Messianic sense", that post-Ulysses, post the Lady Chatterley and Naked Lunch obscenity trials, it was necessary for literature "to keep pushing on".

For years, I suspected this early work was beautifully written psychoporn. Then Fred West entered the national stage and I conceded that McEwan knew more about humanity than I did. Nevertheless, as he points out, he didn't have to know much else. He attributes his ignorance, this deafness to social nuance, to the social deracination of his childhood, largely spent abroad with his father, a noncommissioned army officer who kept company exclusively with the other NCOs. As a teenager he was sent to a London County Council boarding school in the remote Suffolk countryside, where working-class boys from inner-city London were prepared for the posher universities. He did not feel socially at ease until, after Sussex University, he enrolled as the very first member of Malcolm Bradbury's creative-writing course at the University of East Anglia.

In interviews he is always asked to account for the violence of his writing there. Unhappy schooldays, enforced separation from his parents, a difficulty in making friends are the usual suspects. When he tells me, however, that his mother, a cleaner by trade, was a fanatically tidy woman, it occurs to me that while some write in order to impose order on their experience, McEwan may have wanted to bring a little anarchy to his over-orderly background.

Sadly, Rose McEwan's mind, the victim of vascular dementia, has now succumbed to its own chaos. The same fate befalls the novelist anti-heroine of Atonement, although we witness only its earliest stages, which are traumatic enough. "I remember her anguish, my mother's anguish, when she was well enough to know what was happening. Now she's so far gone she has no idea and she's actually much happier, but it's not a happiness she'd want to buy into. Before she was at the let-me-not-be-mad stage. Complete anguish."

If McEwan, who at Norwich stoked his mind with mescaline, LSD and cannabis, originally had to goad his subconscious into throwing up horrible subjects, today, one might say, the horror comes calling. This is what his friend Martin Amis would call "experience", or getting older, but it is also a matter of knowing more history. In two previous novels, The Innocent and Black Dogs, he meticulously located the source of 20th century darkness in the Nazi regime. Atonement's central section relates the retreat from Dunkirk.

"My father was at Dunkirk and he told many stories about it, God yes, especially in his dying years: he had emphysema. He did this three-day walk across the landscape there, although, actually, not all of it was walking. He was a dispatch rider and he got his legs badly shot. He teamed up with a guy who'd had his arms badly shot. Between them they worked the controls of the bike."