BOOK REVIEW / Tangled up in Charlotte's web: Helen Birch on Jenny Diski's latest and best exploration of a singular female spirit: Monkey's uncle - Jenny Diski - Weidenfeld & Nicholson pounds 14.99

THE WOMEN at the centre of Jenny Diski's novels share similar characteristics. Intelligent, professional, ordered. Usually single parents; if not single, then singular in that other people, particularly men, play a marginal role in their lives. All have an intellectual understanding of their gender yet each defies it. Like the clinical, precise prose in which Diski conveys their thoughts and feelings, they are ironic and alienated. If they are unloveable and unloving, it is because love has not rubbed off on them. And they all, in some way, go mad.

Rachel, the rational, independent protagonist of Diski's first, controversial novel, Nothing Natural, found her carefully constructed world systematically dismantled by a sado-masochistic relationship. Mo, of Rainforest, fell foul of her obsession with order and retreated into madness, while another Rachel, of the extraordinary Like Mother, surrendered to nihilism by giving birth to a baby without a brain. Then came Esther, who, unable to connect with anything that might make sense of her life, imagined herself twinned with a heretic from another century; and in Diski's last novel, Happily Ever After, a demented social worker turned murderer.

Charlotte Fitzroy, 49, feminist, single parent, political activist, madwoman, is their natural successor. Her breakdown, like theirs, is not the nervy, emotional sort usually ascribed to middle-aged women, but a 'dialectical hole', into which have fallen the fictions and conventional niceties she has conjured to give her life a point. What she's left with are facts, fragments and patterns stripped of narrative structure - 'a runny continuum of meaning'. Around this existential gap Diski summons ideas borrowed from science, structuralism, psychology and politics, then discards the claims to absolute truth of each one. Madness, for Diski, offers the means to investigate big questions: what happens when belief systems fail? Can a person ever recover from the unhappiness of the past? You get the sense from her novels that if there is such a thing as truth, it hovers somewhere on the borders of sanity.

A few months after the Berlin Wall comes down and her daughter is killed in a car accident, Charlotte is found naked in her garden pulling up all the plants. In hospital she hides her anti-depressants and, determined to 'appear just defeated enough to be both understandable to the doctors and a reassurance to her son' duly describes scenes from her past to Matthew, her therapist.

Charlotte has devoted her life to belief in the 'perfectibility of humanity on a grand scale', and neglected her two children, both the progeny of her affair with a married man, who conveniently died in a car crash just as she was getting bored with him. With shattering honesty she tells Matthew that: 'Of the two fatalities (the death of her daughter and of Communism), it was the loss of my ideals that turned out to be the most personal.' The greatest thinkers of the modern age, Darwin, Marx and Freud have let her down by not being 'good enough'. Along the way, she also confesses to a loveless childhood, after which love simply felt like a game of reassurances.

In her mind Charlotte has split in two. Through this process, Diski gives her light, perverse humour room to roam dizzying intellectual horizons. While Charlotte 'up there' negotiates hospital routine, 'Charlotte-the-Crazed' wanders, like a deranged Alice in Wonderland, in an 'eternal afternoon' of her imagination. She converses with Darwin, Marx and Freud - absurd apparitions who argue in theoretical cliches and whose obsessions with food, the common denominator of life, seem the natural outcome of their reductive thinking.

She also takes tea with Jenny, an orang-utan who wears flowery frocks and a hat decorated with fruit, who doubles both as a quixotic authorial voice and, by way of aphorism - 'manners are what separate the civilised from the savage' - as a corrective to Charlotte's more tangled thoughts. In between, she is haunted by the story of the God-fearing Robert FitzRoy, captain of the Beagle, to whom she believes herself related and whose conviction about his own ancestral doom she shares.

Beyond these prosaic and fantastic extremes of madness, a metaphor takes shape. Charlotte is a genetic researcher, fascinated and infuriated by the ineffable language of chromosomes. She imagines her life viewed through two ends of a telescope - 'the universe end and the particle end' - which she has interpreted as politics and biological determinism. Her fear is that whichever way you look through the telescope, you can only see what is already known, an approximation of the true state of things.

Like Robert FitzRoy, tortured by the impossible task of mapping the South American coastline down to the last, shifting grain of sand, Charlotte experiences the terror of relativism, the absence of any solid connection between life and history, self and others, ideas and people.

Even Diski's critics - and there are many who find her bride-stripped-bare approach hard to accept - would not doubt that hers is an original voice. Novelists who are as comfortable with the discourses of genetics, philosophy, psychoanalysis, linguistics and anthropology are rare. And yet some of her earlier novels have been over-schematic, as if she's set herself a problem and invented characters to examine it. In Charlotte, however, she has created a character who feels as well as thinks, who experiences real pain and real numbness rather than the idea of emotion and its absence. Monkey's Uncle is a marvellous achievement: intelligent, humane and quietly optimistic. It's as if Diski, like Charlotte at the end of the book, has set the telescope aside, and allowed herself to trust what she sees with her own eyes.