Travels beyond the grave: Audrey Niffenegger turns her attention to Highgate cemetery and its ghosts

Audrey Niffenegger likes cemeteries. "It's the combination of rootedness and open space," she says as we sit in the very unsombre forecourt of a Highgate Village pub, surrounded by cheerful people eating their lunch.

"It's the serious, sombre quality of what they are there for and the quirky individualism of some of the graves, and what you find in London's big cemeteries are restrained" - setting aside the quirkiness of a few individual gravestones - "by the side of the strange art nouveau tombs of a city like Milan."

There are still some London cemeteries she has yet to visit. It is almost as if they are treats which she has to ration. Cemeteries fit neatly alongside her other obsessions - fashion and the Victorians. It would almost be insulting to notice the degree to which Niffenegger has the sort of neat, dark, perfectly cared-for style that in a man we would call being a dandy.

Like Robert, the principal male character of her new novel, Her Fearful Symmetry (Jonathan Cape, £18.99), she works as a voluntary guide at Highgate cemetery. While she has not, like him, written an academic thesis on its history, wildlife and post-mortem inhabitants, she knows it well. "Robert sometimes found himself become weightless as he crunched along the paths," she writes. "At such times he felt a powerful sense of rightness; under his body, beneath the grass, the dead were quiet and peaceful in their little rooms."

In this book, Highgate cemetery is at once a thoroughly evoked visual landscape and a social institution; it is also, in a very Dickensian way, the multi-faceted central idea of the novel. Her novels and her art - her original training was as a print-maker, and she still teaches book arts at Columbia College in Chicago - have this same perfectly cared-for quality, the product of slow growth and change. She was two years into Her Fearful Symmetry before she realised that this was going to be a book with a ghost in it, and four before she knew what the novel's quietly devastating climax was going to be.

In due course, she wrote a scene where one of a pair of identical twins, and the ghost of her aunt Elspeth, play with a kitten. She knew all of a sudden where all of this was going to go and just how much of a monster Elspeth had it in her to become.

Some early reactions to Her Fearful Symmetry have complained that it is too diffuse, full of wonderful narrative strands and ideas that do not cohere. This is a strange indictment of a book which, if anything, comes close to being too fixed in its gaze at characters who are trapped in situations that vary from being dead, to being in a relationship that they have tired of, to suffering from obsessive-compulsive disorder.

That her previous novel, The Time Traveller's Wife, has recently been distorted by Hollywood into something that can be sold as a romantic comedy should not be allowed to mislead us. Audrey Niffenegger has a very bleak imagination indeed. In both novels, she examines questions of free will. Neither the time traveller nor his wife have more than the appearance of it, she because he has groomed her from childhood to love him, and he because the adult woman has told him earlier that they are going to be together. There is no force punishing Henry for his attempts to change events; things are, hideously and joyfully, as they are, and he is a slave to his condition.

Nothing in the new book is quite that grim; the only consolation for Henry and Claire is that their daughter, also a time-traveller, is freer than they can be because she is more evolved. Whereas all of the characters in Her Fearful Symmtery have at least the chance of moving on. "People don't seem to get that most of my characters get an ending that is open," Niffenegger says about the new book. "I love the ambiguity of open endings." We don't know whether some characters end up alive or dead, trapped by their sins or freed from them by chance and something that this very secular writer could nonetheless easily call grace, but doesn't.

Even Elspeth ends up at once punished and with some chance of making some things right; her nieceValentina is last seen experiencing a weird kind of joy. "What does happen to people is, though, in most cases what might as well be called karma," Niffenegger says, "a sense that what goes around comes around - but there are also random bad things that happen to people, like Martin's mental illness, no one's fault and the product of bad chemicals."

Niffenegger, for a while, dated a man with a milder version of Martin's obsessive-compulsive disorder. Spending time with someone in that position makes one realise at once how totally it is an illness, and yet also how closely it resembles the small bad habits of our more ordinary lives.

Not everyone in the book is trapped; there are also characters like Jessica, who supervises the cemetery's volunteer guides. Her role is not so much to be caught up in the story as to be its chorus - Jessica is in some measure a portrait from life. However, in the end, as a chorus in what is at least partly a tragedy, Jessica can do no more than observe and occasionally warn; she is, quite literally, only a guide.

Niffenegger, Chicago-born and an MFA graduate in printmaking and drawing from Northwestern University, is an artist as well as a novelist. Two of her books, The Three Incestuous Sisters and The Adventuress, are combinations of narrative and illustration. Her eye for visual detail is part of what makes her novels so precise in their sense of what happens as characters move around a scene. One of the key events of her adolescence was an extended illness in which her mother brought her art books, one of them the Brian Reade catalogue for the crucial 1960s exhibition of Aubrey Beardsley. Beardsley is a presiding genius of Niffenegger's work - his perversity and moral sense, his austere sense of line and his wonderfully closely seen details. She has thought sometimes that she would like to find a way of writing about Beardsley, creating a character who is his modern equivalent.

In her first two books, the images she drew were quite as important as the tale. Part of the evolution of The Time Traveller's Wife was that she thought of characters and a story that she could not tell through illustration, and fragments of text that demanded the length and complexity of a novel. Much as she has come to love the demands of writing novels, she is still fond of the illustrated form, and is considering further experiments with comics. When she did a short comic, The Night Bookmobile, she was amazed how long it took. You have to tell the story through compressed and intense dialogue and art that is hardly ever static. There are reasons why few comics creators are both writer and artist - both roles are so demanding, she suggests.

Does she worry about what Hollywood has made of her first novel? Not really, and she has not even been to see it. "What films make of books is always going to be something quite different from what the author wrote," she thinks; they are separate art forms. When she first read The Wizard of Oz, she was genuinely surprised by how different it was from the Judy Garland film, not just in detail but in overall feel. L Frank Baum's novel was full of satirical comment on political causes that we have for the most part forgotten or ceased to take seriously. Good as it is, the film has colonised our imaginations to an extent that means that the text cannot be read in quite the same way.

Her third novel is currently evolving from a short story; she is working on drawings for an exhibition and going through that slight sense of disjunction that comes when she switches between aspects of her art. She is back in the studio and experiencing a brief period of frustration when her drawings are not quite coming off. It always takes a while, and getting back the full use of a skill takes meticulous work - not just innate talent. "No matter how low your level of skill," she says, "draw for an hour a day and after a year, you may not be good, but you will be amazingly better than you were."