I remember a window in a farmhouse in North Wales which had a sill of white-washed stone so deep I could sit sideways in it at the age of six, hugging my knees to my chin. From that spying place I had a view of the orchard of apple trees behind the house. The orchard seemed large to me at the time, though in retrospect it probably contained less than twenty trees. In the heat of the afternoon the farmyard cats, having exerted themselves mousing, went there to doze, and I went to hunt through the unkempt grass for eggs laid by nomadic hens. Beyond the orchard was a low wall, with an ancient mossy stile. And beyond the wall an expanse of rolling meadow, grazed by sheep, with the sea a misty blue prospect.

I have little way of knowing how accurate these memories are; almost forty years have passed since I was small enough to sit in that window niche. The photographs my parents took of those distant summers are still pasted in the musty pages of their album, but they are tiny, black and white and often blurred. There are, it's true, a couple of pictures of the cats, dozing. But none of the orchard, or the wall, or the meadow: And crone of the window where I sat.

Perhaps it doesn't really matter how accurate my memories are; all that matters is how powerfully they move me. I still conjure that place in my dreams, and when I wake I have the details clear in my head. The smell of the nightlights my mother set on the dresser in my bedroom, the dale beneath the trees, the warmth and weight of an egg, found in the grass and carried into the kitchen like unearthed treasure. The dreams are all the evidence I need. I was there once, blissfully happy. And though I cannot tell you how, I believe I will be there again.

The farmhouse has long since disappeared; the cats are dead, the orchard uprooted. But I will be there again.

If you are already familiar with the book in your hand, you know the relevance of this sliver of autobiography. Weaveworld is a meditation on memory. Yes, it also tells about magic and demagogery and angelic judgments, but the central drama of the tale is the way the characters remember - or fail to remember - the glimpse they've had of paradise.

This, for instance, of Cal Mooney, our hero: ‘It was only when, in the middle of a dreamy day, something reminded him - a scent, a shout - that he had been in another place, and breathed its air and met its creatures, it was only then that he realized how tentative his recall was... The glories of the Fugue were becoming mere words, the reality of which he could no longer conjure. When he thought of an orchard it was less and less that extraordinary place he'd slept in (slept, and dreamt that his life he was now living was the dream) and more a commonplace stand of apple trees... Surely dying was like this, he thought; losing things dear and unable to prevent their passing.'

The novel is not primarily about the escape into Eden. It's about how the knowledge of Eden slips from us, and the means we devise to hold on to that knowledge: This is, I think, a universal experience; which may go some way to explaining why the book continues to find readers. I recently, finished a six-week publicity tour for a new novel, and at book-signings across the country found readers bringing me battered but much-beloved copies of Weaveworld to be inscribed; several times I heard people say the book had helped them through dark times in their personal lives.

There is nothing more gratifying to this author than to sign and personalize a book which has seen some action: passed between friends, dropped in the bath, coffee-stained and sun-yellowed. I have in my library copies of certain works - Melville, Poe, Blake - that I've treasured over the years, all much the worse for wear. I know how close you can get to a book whose stains and creases are part of your shared history. And what more perfect marriage of form and content, than that a novel about memory, like Weaveworld, should be valued because of the events that have marked it? The book was published in 1987, the year in which the first Hellraiser film was released, but it represented a considerable departure from the transgressive horror fiction with which I had become identified. There were plenty of critics ready to snipe at the change of direction, opining that my imagination was too dark for the genre I was attempting to infiltrate, and I was better off staying on the horror shelves. But the response from readers, including many who were devoted to the extremes of my earlier work, was overwhelmingly positive. The book sold solidly from the outset, and has continued to do so, in several languages, ever since. It has sparked off creative work in other media from readers who wanted to explore the story for themselves: paintings, poems, musical compositions; even an opera, planned for production in Paris. I have come to believe that the darkness I imported into the work, far from proving problematic, is very much to the book's purpose. Yes, there are raptures in the novel, and glorious deliriums. But the Fugue - the magic haven of the book - is threatened with total destruction, and the powers that overshadow it are not tuppenny coloured terrors. They are the obscenities of human cruelty and human despair. Tales of Paradise Lost are central to our culture, of course; we are all exiles from some place of bliss.

What is that place? A memory of a pre-conscious state of perfect contentment, where we believe ourselves whole because we have not yet comprehended the fact of our physical separation from our mothers? Or a religious conviction, too deep in our selves to be subjected to the rigours of intellectual enquiry, that knows our connection to the planet, to animal life, to the stars? A faith, is it? Or a glorious certainty? It isn't necessary for a storyteller to have answers to the questions they pose, of course; only to be interested enough to ask them. Weaveworld is full of unrequited enquiries. Why does Immacolata's hatred of the Seerkind burn so intensely? Is the creature in the Empty Quarter an angel or not? And if the garden of sand in which it has kept its psychotic vigil is not the Eden of Genesis, then where did the Seerkind arise from? There are certainly answers to these mysteries to be wrought and written, but they would, I am certain, only beg further questions, which if answered would beg yet more. For all its length and elaboration, the novel does not attempt to fill in every gap in its invented history. Nothing ever begins, its first line announces; there are innumerable stories from which this fragment of narrative springs; and there will be plenty to tell when it's done. Though I get requests aplenty for a sequel, I will never write one.

The tale isn't finished; but I've told all I can. That is not to say my attitude to the work does not continue to change. In the past ten years I've gone through, periods when I was thoroughly out of sorts with the book, or even on occasion irritated that it found such favour with readers when other stories seemed more worthy. And in the troughs of my discomfort, I made what with hindsight seems to be dubious judgments about fantastic fiction as a whole. I have been, I think, altogether disparaging about the escape elements of the genre, emphasizing its powers to address social, moral and even philosophical issues at the expense of celebrating its dreamier virtues. I took this position out of a genuine desire to defend a fictional form I love, from accusations of triviality and triteness, but my zeal led me astray. Yes, fantastic fiction can be intricately woven into the texture of our daily lives, addressing important issues in fabulist form. But it also serves to release us for a time from the definitions that confine our daily selves; to unplug us from a world that wounds and disappoints us, allowing us to venture into places of magic and transformation. Though of late my writing has concerned itself more and more with detailing that wounded, disappointing reality, as a reader I have rediscovered the pleasures, of unrepentant escapism: the short fiction of Lord Dunsany, early Yeats poems, the paintings of Samuel Palmer and Ernst Fuchs.