Wicked, by Gregory Maguire

Subtitled "The life and times of the wicked witch of the west", Gregory Maguire's Wicked falls into a fascinating sub-genre of novels that revisit well-known stories as much in the spirit of criticism as homage. The progenitor of the form might well be Henry Fielding with his Joseph Andrews, an alternative take on Samuel Richardson's Pamela, but modern examples include Jean Rhys's Wide Sargasso Sea, about the early days of Mrs Rochester, and Jan Needle's Wild Wood, the Wind in the Willows story from the stoats' and weasels' perspective.

Like these writers, Maguire upends the moralities of a classic - here, L Frank Baum's The Wonderful Wizard of Oz. He draws on elements from the sequels Baum wrote to his original, but also tells a story that reads just as well for people who only know Oz through the Judy Garland film. Baum, writing a fairy tale for children, sketched his Oz leaving blanks to be filled, populating his fantasy world with talking animals, Munchkins, witches, flying monkeys and whatever else came to mind. Maguire, a century later, makes sense of Baum's whims, creating a credible Oz for grown-ups, with religion, politics, racial tensions, an economy, mythology, humour and sex. Often, Baum's lax plotting spins off into affecting stretches of story.

Like Rhys and Needle, Maguire takes the point of view of an apparent villain. He fills in a back story, leading us to question what really is so wonderful about the hypocritical, despotic Wizard, and why the citizens of Oz see-saw so oddly between outbursts of joy and a creeping fear, which has rendered even a lion cowardly.

We follow the water-intolerant Elpheba from babyhood in Munchkinland through education in a university town - where she picks up a sense of the injustices encouraged under the Wizard - to young womanhood, torn between a love affair and work for a revolutionary movement, and exile in the West. Along the way, Elpheba becomes a true Wicked Witch, and also a genuine heroine. This makes the last section of the tale - from the death of Elpheba's sister under a falling house to her own melting-away - as moving and tragic as it is refreshing and scurrilous.

It has unaccountably taken 10 years for this outstanding novel, the inspiration for a hit musical, to be published in Britain. Although the UK edition lacks the woodcut illustrations of the American first edition, it wins points for an eerie, effective gilt cover.