The Last of the Duchess, Hampstead Theatre, London

If the mere thought of Madonna's reportedly flattering biopic is enough to induce severe Wallis Simpson fatigue, please don't let this put you off The Last of the Duchess, the delectably funny and haunting new play by Nicholas Wright.

In bedridden reclusive widowhood in her Bois de Boulogne mansion, the Duchess is a tantalising off-stage presence here and the focus shifts intriguingly to the surrounding retinue who were out to protect and/or exploit her.

The piece is based on Caroline Blackwood's sharp, darkly humorous book of the same name. Commissioned in 1980 to write a Sunday Times profile, this distinguished author and Irish aristocrat found all avenues of access blocked by Maitre Suzanne Blum, the Duchess's formidable octogenarian lawyer and gatekeeper. In certain respects, though, Wright's play outstrips its source. It is able to take a completely detached, quietly hilarious look at the operations of snobbery and, by subjecting Blackwood's own methods and motives to sceptical scrutiny, it offers astute insights into the relativity of truth.

The central battle of wills is conducted with a terrific tragicomic force in Richard Eyre's splendidly cast and consummately witty and stylish production. Anna Chancellor is perfect in the role of Lady Caroline, radiating raffish toff's confidence, while guzzling vodka and wrestling with her private demons. As Blackwood's fellow Irish expat and Blum's prize protégé, Michael Bloch, the wonderfully amusing John Heffernan brings out the shrewd, sympathetic side of this slightly fey and fawning courtier. He argues that Blackwood, having been variously interpreted in paint and in poetry by former husbands Lucian Freud and Robert Lowell, should know that people can never be definitively captured. But Blackwood is determined to view the situation as a Gothic horror story in which a demon has imprisoned and isolated the Duchess, prolonging her life for her own warped and selfish ends. She is reinforced in this prejudice by the stories of missing jewellery that turns up anonymously at auctions told to her by Angela Thorne's charming and unrepentantly anti-semitic Lady Mosley.

A superb performance from Sheila Hancock keeps you guessing about Blum. She's a control freak and howling snob who melts at the thought of being photographed by Lord Snowdon. She's an intelligent, self-made lawyer and a fantasist who fiercely guards the interests of a client she has turned into an object of obsessive love, even at one point imitating her pose at the mantelpiece. A gem of a show, warmly recommended.

To 26 November (020 7722 9301)