The Lady and the Unicorn By Tracy Chevalier

Have you ever wondered about woad, and why those who wore it seemed so menacing? The answer, according to Tracy Chevalier's researches, lies less in its appearance than its intolerable smell. Woad was powerfully foul. To stabilise the blue colour of his dye, the woad-merchant used fermented sheep's urine: the aroma preceded him everywhere and few could bear his company. Thus woadmongers could attract mates only from within their immediate families, with the result that succeeding generations became increasingly unappealing.

This is one of those classic Chevalier byways, first used to great effect in Girl with a Pearl Earring. Having set up a racy story, she takes us aside for a purposeful moment, so as to instruct us in arcane customs, then she returns us briskly to the plot before we begin to feel that we're being lectured. She does it by having her characters give us, in their own voices, the long-lost details of their ordinary lives, as if they were presenting reliable evidence to a court, say, or a priest. We trust them to tell the truth though they know only their side of the story. And, since the past is always coloured by opinion and Chevalier makes no claim to omniscience, we are generously and properly allowed to draw our own conclusions.

Jacques, the disgusting woad-seller in this latest novel, wants to marry Aliénor, the blind daughter of a Brussels weaver, to bring new blood into his inbred family. Her rescue comes in the form of a consummately priapic Parisian artist who arrives in her father's workshop with preliminary drawings for a series of tapestries. Nicolas des Innocents is a swaggering lad, talented and charming. Originally commissioned to produce bloodthirsty battle-scenes, he persuades his patron to allow him instead to illustrate the mysterious legend of the unicorn - a creature only to be tamed by a chaste maiden. It is a story he himself habitually uses as a seductive ploy.

Nicolas is our (flawed) hero. His voice begins and ends the book and it is his sexual appetite that drives it on. Chevalier gives him a quaint vocabulary - he boasts of being happy to "plough" three times nightly - but then Claude, his patron's bold and nubile teenage daughter, is similarly libidinous: "The sound of his voice went straight to my maidenhead," she gasps. Clearly the only safe place for her is a convent, whither she is duly, if temporarily, despatched: Aliénor's fate is earthier.

But Chevalier's gift is not limited to undercover education and the creation of lively characters. What she does best is to study a famous work of art with the eyes of a bright, inquisitive child, teasing out a story that might lie behind it. Then the more academic adult takes over and weaves, with Brussels skill, an intricate background and a plausible plot. The marvellously enigmatic medieval tapestries of her title, reproduced on many a cushion-cover, are a gift to this, her own brand of historical fiction.

In this book, however, for the first time she allows herself to play a little with her reader, teasingly suggesting the anachronistic. A servant, for example, is sent out to buy sweet cakes for the visitors. Four hundred years before Proust, her name needn't have been Madeleine, but it is.