Now that's what I call losing the plot

Charlotte: the final journey of Jane Eyre by D M Thomas (Duck Editions, £14.99, 173pp)

Prequels and sequels inspired by the classics are popular with readers who want to know what happened to their heroes and heroines before, or after, the existing confines of the narration. In Wide Sargasso Sea, one of the most successful prequels, Jean Rhys told the story of Rochester's first wife, cleverly picking up on clues supplied by Charlotte Brontë in Jane Eyre and creating a novel that stands completely independently. In Charlotte, D M Thomas does something more audacious: he entirely re-writes the ending of Jane Eyre. Taking Brontë's final chapter and, cheekily, extracting whole paragraphs, Thomas turns much of Jane's own testimony round, often contradicting it.

As every Reader knows, the prim passionate governess married her man. By the time, Jane Eyre sat down to pen her story, she has already enjoyed 10 years of married bliss. The blinded Rochester has regained his sight sufficiently so that "when his firstborn was placed into his arms, he could see that the boy had inherited his own eyes, as they once were - large, brilliant, and black". Jane's cousins, Diana and Mary Rivers, have both married happily and respectably and St John - who took the news of Jane's marriage to Rochester stoically - has devoted his life to spreading the gospel among the heathen in India. Everyone is happy and, after all the emotional turmoil, most readers are content that they should be so.

In Charlotte, Thomas presents a much more realistic version of events. His Jane is so painfully pure that, even though she relishes the delights of the marriage bed, she is shocked to discover later that her marriage is, in fact, unconsummated. Men doing things with their hands do not produce babies. "I was still a virgin... It was unbearable, to have been so stupid. Unbearable, above all, not to have been able to stir the least desire in my husband." When she tries to discuss his impotence with Rochester, he rides over the moors to seek consolation with Grace Pool, and breaks his neck in a riding accident.

Instead of 10 years of married bliss, Thomas's Jane only enjoyed two. When she had written to her cousins Mary and Diana Rivers telling them of her marriage and inviting them to stay, Edward Rochester surreptitiously read his wife's letter (with a magnifying glass) and then demanded to know why she lied to her friends - suggesting he concurred in her invitation when he would prefer not to have them near.

When Charlotte Brontë wrote Jane Eyre, she was well-versed in passion and unrequited love, but in no position to write about sex and marriage. It was only later, after her marriage to her father's curate, Arthur Bell Nicholls, that she famously discovered the joys of sex. She wrote about them ecstatically to her penfriend, Ellen Nussey. Nicholls was annoyed at her revealing the intimate details of their lives to her friend, and tried to put a stop to the correspondence. In the light of this, I suspect the more experienced Charlotte might herself have found D M Thomas's version of Jane's married life somewhat more authentic than her own.

Not that anything in this hilarious literary romp is quite straightforward. The revised ending of Jane Eyre turns out to be the work of a Miranda Stevenson, a women's studies lecturer fleeing her computer-consultant husband, who works in the Dome, and giving a lecture on Brontë to a conference in Martinique. The hotel courier mistakes her for a professer called Charlotte Brontë, lecturing on the novelist Miranda Stevenson. Miss Brontë thus has sex with wine waiters and transvestites, as well as with a plantation worker who comes complete with machete, and whose girl is proud that he can attract a white woman.

The whole exercise is a wickedly irreverent antidote to earnest study, but I shall not be bestowing it on my niece, reading Jane Eyre for A-level. Although I am certain she would prefer this version to the original, I do not want to be blamed if she quotes "Reader, I told him to piss off" in her exam.