Blackbird, Oxford Playhouse, Oxford

David Harrower's Blackbird won the 2007 Olivier Award for Best New Play against stiff competition from Frost/Nixon and Rock'n'Roll. But anyone watching David Grindley's superb touring production will not think that it was a wayward choice. This taut two-hander about abuse, obsession, wrecked lives and incurably illicit desire is a devastating feat of sustained and morally unsettling ambiguity. And, for my taste, the new production packs a heftier punch with its unshowy intensity than Peter Stein's arty, more self-conscious original staging.

When she was 12, Una had a three-month sexual relationship with Ray, a man of 40. He has since served a prison sentence, changed his name to Peter and attempted to salvage his life. Now, 16 years on, she tracks him down to the bleak, litter-strewn locker room of the nondescript factory where he works.

At first, Dawn Steele's Una is ablaze with savage scorn as she subjects Ray to a detailed account of his crime. But then it becomes clear that the even deeper source of her wounded anger is his betrayal when he abandoned her in a Tynemouth B&B as they were about to elope to Europe together. As Steele's excellent performance harrowingly indicates, the experience has left a Ray-shaped hole of howling need inside her, with the feelings of a jilted lover and of a frightened, deserted child hopelessly entangled.

Without in any sense condoning his actions, the play refuses to sit in easy judgement on Robert Daws's paunchy, desolately abashed Ray. Instead, it dangles a question mark over him, which tilts this way and that as sympathies shift. He contends that the pre-teen Una had a precocious understanding of adult love and that she pursued him. He fervently maintains that he is not a paedophile and that she is the only minor with whom he has ever meddled. His apparent desertion of her was a chapter of tragic accidents. Theirs was a love out of the ordinary.

How much of this is true and how much of it is what they both now need to hear? The play suggests that these are matters that, at this distance, cannot be definitively resolved, showing you a couple who have become ghosts in their own lives, unable to escape from the deforming time-warp of their brief affair.

Towards the end, a third character appears with truly shocking effect, re-opening all the uncertainties. Lethally well-paced, Grindley's production holds the audience mesmerised for the hundred minutes of unbroken playing time and firmly establishes Blackbird as a modern classic.

Touring to 14 June ( http://blackbird.binarylab.com )