Blackbird, King's Theatre ***** <br></br> Nymphs & Shepherds (A Paedophile's Life), Club Ego, Picardy Place, Edinburgh **

When the dark truth comes home to roost

Blackbird, a Festival commission, seems a long way from David Harrower's impressive first play Knives in Hens, dealing with bad feelings in the Scottish grain business centuries ago. Here, Harrower sets out to "test the limits of the moral world," as he puts it, exploring the feelings (and the audience's) between a man and a woman with a past. Ray, now 56, was convicted 15 years earlier for his sexual relationship with 12-year-old Una. He has forged a new identity and a fresh life, but Una, now 28, forces an unexpected and unwanted encounter.

These characters are very fragile, on the verge of crumbling as the dark secrets of their relationship are penetrated and the layers of their three-month liaison peeled back until both are raw with emotion. The recesses of their minds are pierced in Harrower's rich, textured writing. Old feelings resurface, and guilt and resentments mingle.

In two extraordinarily intense performances, Roger Allam as Ray and Jodhi May as Una confront what they experienced then and what they feel now, and the voids they felt on being parted. Peter Stein's direction is subtly undemonstrative, illuminating the apparent transparency in Ray's attraction to Una - his "stupid mistake" - and her childish eagerness to be his girlfriend; her "suspiciously adult yearnings," as the judge had put it.

Exquisitely judged detail adds to these performances. Allam slumps like a crumpled doll, May gesticulates; they circle each other, body language speaking volumes.

Neither condoning nor condemning, Harrower has produced a fine, thought-provoking piece on a taboo subject. I am not going to reveal either the worrying revelation that comes near the end, or the coup de théâtre that brings the curtain down on these troubled lives.

In his Fringe play Nymphs and Shepherds (A Paedophile's Life), David Hines explores what drives a man to paedophilia, putting his protaganist's thoughts and motives under unpleasantly close scrutiny as he ruminates on his sexual awakening and many intimate encounters with young girls. An angry mob is at his door, and he's waiting for the police to move him to yet another safe house.

It's a bold if overlong monologue, brilliantly delivered by Barold Philips, but unnecessarily graphic and repetitive in its description of the paedophile's pleasure.

'Blackbird' ends tonight (0131-473 2000); 'Nymphs' to Monday (0870 241 0136)