Wild Mary: a life of Mary Wesley, by Patrick Marnham

Nine months before her death in 2002, Mary Wesley authorised Patrick Marnham to write her biography and handed him two shoeboxes containing her correspondence with her second husband, Eric Siepmann. "Both shoeboxes were marked size 5," Marnham recalls. "The newer ones carried a price tag of £300, the other - dated 1973 - was priced at £4.50." As this well-chosen detail nicely demonstrates, Wesley may have died rich and successful, but she achieved this only during the last two decades of her long life; before that she had spent many years living on very little indeed.

Her first novel, Jumping the Queue, arose out of Wesley's genuine despair after the death of Siepmann. A black comedy about a lonely widow in her fifties who decides to commit suicide, it had been turned down by a succession of dim publishers on grounds of its "general morbidity" and "off-beat" characters. Its eventual acceptance encouraged Wesley to continue writing, eventually clocking up ten titles and huge sales.

Her career really took off with the much-loved The Camomile Lawn (1984), the story of five young cousins dividing their time between blacked-out wartime London and a large house in Cornwall. It may not have been high literature (Anita Brookner, described here as "the Sisyphus of the Fulham Road", was particularly sniffy), but it had considerable narrative drive, was sexy, funny, cleverly structured, and provided sophisticated entertainment.

Subsequent novels reintroduced such themes as "the ideal house", incest, illegitimacy, death by water and "the elderly seducer", while characters occasionally reappeared, so that the Wesley oeuvre had a certain coherence. It would be unfair to say that her readers knew what to expect, since she was always capable of providing surprises (usually nasty ones), but she created a recognisable and attractive fictional world.

In this lively biography, Marnham sensibly avoids literary criticism, concentrating instead on the rackety life that fed into the novels. A neglected child who always felt she came a poor third to her older brother and sister in their parents' affections, Mary Farmar was educated at home, managing to get through 16 governesses and earning the nickname that gives this biography its title. Her childhood was peripatetic: her parents moved house 27 times during their first 25 years of marriage. At one point, when Mary was 14, her mother dumped her in a hotel in Brittany and disappeared for three months.

It is hardly surprising that Mary became wild and a frequent embarrassment and worry to her parents. On one occasion she explained away her unfortunate discovery in bed with one of Lord Baden-Powell's sons by saying they were "keeping warm"; but she soon outgrew boys and started scouting for men.

She was presented at court and embarked on the social round of country-house dances and grouse-shooting in Argyll. She was eventually bagged by a rich young peer called Carol Swinfen, but the marriage was not a great success. Unlike his wife, Swinfen was not much interested in sex, and he fondly accepted Mary's second son as his own even though he almost certainly knew that he was not the boy's father. In a book characterised by bad behaviour of one sort or another, Swinfen emerges rather well.

Mary's wartime experiences (during which she worked in intelligence and got through innumerable lovers) will seem familiar to readers of The Camomile Lawn. Marnham is very good at the sort of offhand remark that both sums up the mores and mirrors the attitudes of the period, as in his aside about one of Wesley's foreign suitors: "He had found it hard to take British society seriously since the day he found his first wife in bed with his mother".

Wesley herself was clearly not an easy woman, but her life was often difficult. She and Siepmann, both struggling writers, endured a prolonged campaign of stalking and intimidation by his first wife, while Wesley's atrocious sister (who once pushed her off a pier) married a crook who meddled in the family finances, provoked an unpleasant court case, and made everyone's life a misery for a number of years. The father of her second son was killed in action (as were other lovers), and Siepmann, suffering from Parkinson's disease, eventually committed suicide.

Marnham becomes slightly muddled and repetitive during the final chapters dealing with Wesley's success. He nevertheless unpicks the complicated web of deceits and half-truths that surrounded much of her life with wit, patience and skill, providing just the sort of compelling read that Wesley did in her novels.

Peter Parker's life of Christopher Isherwood is published by Picador