Concluding to her final piece of unfinished business for Paines Plough, the director of the new National Theatre of Scotland, Vicky Featherstone, directs David Greig's sparkling new play about the nature of self. Yet, as deep, meaningful and thought-provoking as the production may be, it is essentially a comedy with serious face.

What first hits you, though, is the attention to detail. As Frances Grey's tightly skirt-suited Anna sits on a Pyrenean hotel terrace preparing to interview Hugh Ross' mildly disturbed elder Man, each new fragment of their conversation makes you desperate to hear more. Delicately, in lines that are almost excruciatingly real, the facts build a complex picture. Pieces in a puzzle that you long to see the whole of. He is a pilgrim, who lost his memory and was found almost frozen in the snow. She is a young attaché to the British Consul, sent to find out whether he is their responsibility or not.

Here on the terrace, anything can happen. Jonathan McGuiness' strangely unnerving Proprietor could be anyone. He might, even, be one of the many different characters he says he is. Across the chasm of the valley, they can see climbers, ant-like, on the cliff face opposite. Every so often, the Proprietor tells them, a climber will fall. And so too, it seems, might one of these characters be liberated from their former selves.

What is certain is that what ever happens will concern Vivienne, played by Paulo Dionisotti, the third visitor to the hotel who spends her time in solitary walks through the pine forests. While Dionisotti's creation of a middle class Edinburgh woman is beautifully controlled, her bizarrely swinging accent is the play's single uncalculated distraction.

All the other distractions, from the postcards hidden in Neil Warmington's set to Nick Powell's music which appears, at first, to swell rather too mawkishly for comfort beneath the conversation, are actually precisely hidden clues and triggers to the whole. And when all is done, although you know who these people think they might be, you learn that it is as likely as not that all the pieces which have gone to creating that picture come from a completely different puzzle all together.

A thoroughly fascinating production, in which the acerbic comedy in the lines just keeps bubbling to the surface - and whose meaning will linger and change over time.

- Thom Dibdin (reviewed at the Tron, Glasgow)