My Arm, BAC London

Competitive tests of endurance - who can hold his breath or stare without blinking the longest - are a normal part of childhood, quickly provoked and as soon forgotten. But to stake your identity on sustaining such a footling feat might be considered excessive. This, though, is the fate of the young Isle of Wight lad in Tim Crouch's strangely haunting and hypnotic solo show.

Competitive tests of endurance - who can hold his breath or stare without blinking the longest - are a normal part of childhood, quickly provoked and as soon forgotten. But to stake your identity on sustaining such a footling feat might be considered excessive. This, though, is the fate of the young Isle of Wight lad in Tim Crouch's strangely haunting and hypnotic solo show.

His was a humdrum, mid-Seventies existence until one day, when he was 10, he decided to raise his arm in the air and never lower it again. A pain in the neck for his parents, social workers and psychiatrists, the gesture is a pain in the arm (and worse) for the boy, but it also feels good. For the first time, he has a sense of setting the rules and of being sharply delineated. The weeks stretch into months, into years. The petty bet with himself turns into a statement and, after he has drifted into purposeless adulthood, then becomes imbued with other people's idea of significance, when the protagonist and his predicament are taken up by the fashionable art world.

You might have expected that the author-director-actor - a gently courteous, sweet-faced presence - would perform the hour-long monologue with arm raised in imitation of (and salute to) the character. But in fact the show - which Crouch presents with such understated confessional candour and such touching self-bemusement that you're lulled into the absurd belief that this is straight autobiography - plays tricksy games with representation.

At the start, Crouch borrows personal belongings from the audience - driving licences, keys, tissue boxes, etc - and, filmed by a video camera and flashed up on screen, these everyday items act out the charged situation, my own black roll-up brolly giving a vividly baleful performance as Mrs Williams, the boy's first shrink. The hero himself features as an Action Man doll. The idea seems to be that there's a parallel between our readiness to invest inanimate objects with personality and the public's desire in the monologue to attribute mythological meanings to the stubbornly upraised arm. There's a favourable contrast here with Edward Albee's play The Man Who Had Three Arms. The third arm in Albee's drama is a bloodless symbol, standing for the current vapid qualifications needed for fame.

In My Arm, though, the limb is felt throughout to be an endangered organic entity. Indeed, never more so, ironically, than when it's freighted with abstract notions. "I had rotted. I had composted from the fingers down," he declares, relating how it's too late now even to have the amputation of the entire arm and shoulder that had earlier been recommended. His final months will be the perfect morbid symbiosis between exploitation and financial protection. The attention-seeker in him will reach a kind of apotheosis.

"Art is whatever you can get away with" is his artist friend's motto. And Crouch wryly writes this out on a placard for us. At another point he talks about how his hair was shorter then, and you can't help but register that Crouch is completely bald. The piece at once encourages a documentary identification between perform-er and subject, and keeps hinting that it is not an unproblem- atic reflection of reality.

The curious thing is, rather than push the audience to a sceptical distance, these little alienation effects merely emphasise the magnetic power of the terrific story.

To 11 July (020-7223 2223)