As You Desire Me, The Playhouse, London

Focusing on the predicament of a woman who has lost all memory of her former life, the piece makes serious play with such familiar Pirandellian preoccupations as the slippery, elusive nature of identity and the relativity of truth.

Scott Thomas is first seen as the amnesiac Elma, a cabaret singer in a sleazy Berlin nightclub ten years after the First World War. The actress is brilliant at letting you see how this flashy, bisexual identity is the contemptuous improvisation of a woman left to the mercy of the market.

She's intrigued and disturbed when a man appears and tells her that she is, in fact, Lucia, an Italian aristocrat's wife, missing since she was gang-raped and abducted by invading soldiers. Reclaimed like a piece of unlabelled left luggage, she abandons her insanely possessive novelist lover, Salter (a growling, George Grosz-like figure in Bob Hoskins' not terribly convincing performance), and moves to Italy in the hope this rescue will be more than a dream.

But her new existence is beset with problems. It emerges that the husband Bruno (Richard Lintern) has a vested financial interest in endorsing her authenticity because the estate that was his wife's dowry is otherwise about to pass to her sister. Determined to prove that she's a fake, Salter arrives from Berlin with a pitiably ravaged and mad woman he's tracked down in an asylum who has certain claims to be the long-lost Lucia. The criteria for verification are indeed treacherous.

As the Scott Thomas character concedes, the real wife would surely be unrecognisable after the ordeals that she has been through. The fact she was identified counts as evidence against her.

In summary, this may sound rather abstract, but Pirandello's great gift is for (as he put it) "converting intellect into passion". In her extraordinarily accomplished, witty and moving performance, Scott Thomas, with her bony beauty and nervy aplomb, shows you a woman who longs for a cleansing, fresh start and who knows that there is a sense in which creating a new, ideal Lucia, constructed according to Bruno's desires, establishes a higher truth than that which can be checked forensically.

Disappointed in his failure to make that imaginative leap, Scott Thomas's heroine presides with a piercing, droll sadness over the discrediting of her own claim. Teasingly, though, she keeps you guessing about its validity, which remains forever ambiguous, as she heads back to the suicidal decadence of Berlin.

Presenting a play permeated by doubt, Kent's production - an unbroken 80 minutes - is, without question, the genuine article.