TALKING to Tim Crouch is like trying to skirt a minefield. You're aware there are all kinds of pitfalls. You tip-toe gently and hope neither of you will blunder into the trap of theatrical pretension.

It's lunchtime on one of the hottest days of summer, a week since July 7. We're sitting in a pub in Barnes. The Thames beside us is still as a mill pond. In the stifling upstairs "ballroom", I have just witnessed an extraordinary event, a preview of Tim's latest Edinburgh excursion, an oak tree, now running at the Traverse. Several times I have been near to tears.

Several times I have felt distinctly uneasy. I have also been aware of a growing hostility towards him as the central, leading figure whose persona as part-hypnotist, partdirector has seemed to me the ultimate in manipulation.

I am deeply suspicious. Yet, when I come to talk to Tim afterwards, I am beguiled by his openness, his honesty. It's a conundrum, as is an oak tree.

Two years ago, Crouch's fictional autobiography, my arm, took the Edinburgh Fringe by storm. Although a performer for 10 years, it was Crouch's first exploration with the notion of theatre as the art of suggestion. An oak tree, however, takes things much further. Inspired by British artist Michael Craig-Martin's 1973 conceptual artwork in which a glass of waterwas "transformed" into an oak tree - best not to ask how exactly; we'll get into all sorts of quagmires about conceptualisation, life, death and theatre (of which more later) - what you most need to know is that Crouch has taken Craig-Martin's initial notion and embroidered it.

That's to say, he's theatricalised and humanised it. If I tell you that Crouch's an oak tree is like being at a seance, that wouldn't strictly be true. If I tell you, however, that it involves a certain degree of improvisation and casts a strange spell, that most certainly is the case. And when I tell you that it's all harnessed to a story of loss and bereavement - a father has lost his young daughter in a car accident - you will see its potential for stirring up a whirlpool of emotions. Add to that a highly theatrical, some might say sensationalist or at least publicity-conscious, conceit, and you have the ingredients for, I can tell you, something unnervingly close to the bone.

Each night a fresh actor is introduced as a "volunteer" to play Andy, the father, and to accompany Crouch, who is definitely losing it. Crouch-hypnotist also emerges as the man who killed Andy's daughter, Clare.

Many stories, many different levels, you will now be appreciating, are intertwined. If you attend, you will find yourself hurtled into this disorientating world of intermingling realities and illusions, where you know you're being manipulated (aren't we always in theatre? ) and where Crouch to all intents and purposes appears to be controlling events.

Yet I, for one - sceptical, hostile, troubled as I was - was sucked in and deeply moved.

Would you buy a second-hand car, nevermind your psyche, from this man? No, you wouldn't.

Crouch's stage persona is creepily attentive, devious - a showman shaman-cum-therapist.

All of which, when I confronted him at the end, Crouch defends with splendid rationality and patience. No, he's not exploiting the current fashion for theatrical mind-bending. And, yes, he's delighted at my brickbat responses.

He's fed up with "psychological realism". He would much rather audiences at least feel something rather than nothing. "Unease is not an emotion I get often in the theatre and I like it, " he says.

"I'd rather have that visceral response to something than just sit through a piece of theatre that's been made by people who are making theatre."

To that extent, an oak tree is a piece made in his own image.

Indeed, he even describes himself in it as "a 41-year-old, balding, with a red face and slouched shoulders".

And he totally rejects my accusation of an oak tree being a display of the ultimate in egotistical control. "I really am opening it out to it all going horribly wrong, " he counters.

Crouch, however, is far too expert and the concept is crafted (with poet-artist a smith and co-director Karl James) with great attention to detail. Given the fragile collective unconscious at the moment, it's anyone's guess what different responses Crouch's clever, getting-under-the-skin approach may engender. I suggest it will be lively. Crouch positively beams.

an oak tree is at the Traverse Theatre until August 28.