In a room above a pub, a stage hypnotist is dying on his arse.

Ever since he ran over and killed a girl he has lost his power of suggestion, and tonight nine of his volunteers are returned to their seats.

The tenth, however, appears to be doing everything the hypnotist tells him to.

Three months ago this man lost his daughter in a car accident, responding to the loss by imagining she has become the oak tree next to the spot where she died. He has come to the hypnotism act looking for answers.

Couching themes of art, loss and human suggestibility in a vivid and absurdly comic narrative, this remarkable piece of theatre is the latest play by Brighton actor Tim Crouch, the man behind last year's Festival success I Banquo.

The inspiration was Michael Craig-Martin's 1973 work in which the artist asserts that a glass of water sitting on a shelf is actually an oak tree.

The outcome, meanwhile, is a bold experiment in theatre form: While Crouch always plays the hypnotist, every night the part of the father is played by a different actor who knows nothing about the show prior to curtain-up and receives instructions as the play goes along.

"There's a nice play between the father volunteering for the act and the second actor volunteering for my show," explains Crouch.

"Someone who has lost their compass in life is played by an actor who has lost their compass on stage.

"We always said if it felt like just a trick we'd ditch it. But the story is better told because there is someone in it who doesn't know what's going to happen next."

Although they always play a 46-year old father who is 6ft 2in and has a blood-shot eye, the second actor may be a man or a woman, big or slight, of any age and colour. They will also range from big names to complete unknowns.

Armed only with an earpiece and an unthumbed script, they have to trust in Crouch, placing them, as he observes, in "a very similar level of release as would be found in a stage hypnotism act".

"I've had amazing responses from people who've done the show," he says.

"People who've never been able to cry on stage have found themselves in floods of tears and some performers have worked so well I've been moved to tears myself.

"Other actors have just laughed their way through the show. There's lots of humour in it and, because it's so playful, when the emotional content suddenly appears it's like a huge slap in the face."

At the heart of An Oak Tree is a fascinating connection between the operations of hypnotism and theatre, as both encourage us to believe in things which are manifestly not true.

But Crouch - groundbreaking dramaturge that he is - doesn't want to get bogged down in philosophising.

"On many levels An Oak Tree is almost childlike in its simplicity," he says. "What I'm doing is ultimately what little children do, which is engaging somebody else in imaginative play.

"It's like, 'You be him and you say this and stand over there and do that'.

"Then we have the interval and go and have our tea, and when we come back we pick up where we left off."

For review, see Thursday's The Argus. On Sat, May 20, Crouch will also host a workshop about the role of the audience in the creation and interpretation of theatre. Call 01273 709709 for details.

Until Sat, May 20. Starts at 8pm, tickets cost £10, call 01273 709709.