Lifegame, Cottesloe, National Theatre, London

Improbable Theatre's Lifegame, a format devised by Keith Johnstone, is a chat show with a difference. Each night, a different member of the National Theatre staff (and not necessarily a famous one) appears on stage with six actors and two musicians and is asked questions about their formative and memorable life experiences. From time to time the chat show is halted, and the company improvise scenes from the tale.

Improbable Theatre's Lifegame, a format devised by Keith Johnstone, is a chat show with a difference. Each night, a different member of the National Theatre staff (and not necessarily a famous one) appears on stage with six actors and two musicians and is asked questions about their formative and memorable life experiences. From time to time the chat show is halted, and the company improvise scenes from the tale.

According to the programme note, the company "happily admits Lifegame doesn't work every single time, the alchemy sometimes fails to materialise." I left with the feeling that I may have witnessed one of those nights - but there is still much to recommend. This reviewer must confess to a fleeting reality TV generation disappointment when the volunteer was not immediately put through the schadenfreude-inducing mill. It is to their credit that the performers never turn the Cottesloe into a comedy club bear pit - even if there are times when the evening flags and a quick and easy gag seems like just the fillip the show needs. But the patient approach is bold and brave and for many of the duller moments - inevitable with such a format - there is often a startling and delightful pay-off.

Richard Eyre had been the previous night's guest, but tonight it was the turn of Tony Harley, the NT's health and safety officer. Not a natural performer - and why should he be? - Mr Harley was a why-say-two-words-when-half-a-one-will-do kind of a guy, but with gentle coaxing he grew into the night relishing his own bravery as he swallowed his stage fright as well as his key role.

At one point our volunteer had a foam rubber mask constructed on his face (a long process) and was asked to portray his own grandfather. Hismask proved liberating and he entered into the improvisation with gusto. With his new found confidence and a supportive cast and audience willing him on to succeed, some good gags and touching moments were elicited. But what came over most powerfully was an exhilarating synergy between audience, subject and performers.

The performers are the show's own safety net. Even when the subject matter yields slim pickings, they are witty and inventive. The stage is free of the smugness that could so mar such an evening left in the hands of comedians alone, and is replaced instead by warmth, inclusiveness and a desire to communicate a vivid tale.

The storytelling is taken seriously, but there's playful-ness in the evening. With the National so often the centre of controversy over not enough new scripts, the wrong kind of old scripts or too many musical scripts, it's a liberating experience to throw the script awayand take delight in a night of raw theatricality. Regardless of how hit and miss that night may be.

To 13 May (020-7452 3000)