Theatre: OBSERVE THE SONS OF ULSTER MARCHING TOWARDS THE SOMME King's Theatre, Edinburgh

Patrick Mason directed the 1985 world premier of Frank McGuinness's Observe the Sons of Ulster Marching Towards the Somme in the Abbey's studio theatre. The moving, sunny, meticulously lucid production he has brought to this year's Edinburgh Festival is his 1994 mainstage revival to mark the declaration of the ceasefire in Northern Ireland. The appropriateness for the work on this occasion was impeccable, since it is a feat of imaginative yet stringent bridge-building. A Catholic from the south, he manages to get inside the skins and the mentality of a group of Ulster men to produce a drama that is both an affecting elegy for the courage of the 36 (Ulster) Division who died at the Somme, and a clear-eyed scrutinising of the bloodlust and death-wish that is their cultural inheritance.

Filtered through the memories of the now aged sole survivor of that day, we follow the fate of eight Ulster volunteers from the joshing camaraderie and needling antagonism of their barrack initiation to the moment of their swapping lodge sashes as they prepare to go over the top. The main character, Piper (excellent Peter Gowen), is a sculptor, a self-hating black sheep of a Protestant ascendancy family and a repressed homosexual attracted to Conor McDermottroe's likeable Craig, a young blacksmith from Enniskillen. Also falling into pairs are two friends from Coleraine (Gerard Byrne and Patrick O'Kane), a couple of Belfast tough-nuts (Frank McCusker and Lalor Roddy), and a half-Fenian (David Parnell) who goads Sean Campion's uptight, self-lacerating lapsed priest into a fit of blasphemy, making him see that he is no better than the rest.

As well as bringing a double focus to bear on these men (allowing compassion for their destiny to mingle with grave misgivings about the culture that formed them), the play proceeds in a fusion of tragedy and comedy. There's a very funny scene where they try to keep their spirits up before battle by performing a piggy-back replay of the Battle of the Boyne. Quite forgetting ideological purity, the pair pretending to be King James stubbornly refuse to be felled and it's the couple impersonating King Billy who come unstuck. The horseplay takes a bitter turn when one of the Belfast men thuggishly intonates that Piper might have allowed himself to fall as a deliberate act of disrespect. Faced with this lot, you would marginally prefer to be a German than a Fenian.

The history that repeats itself farcically in that piece of tomfoolery is also the recycled history that propels these men to their death. "In the end, we were not led, we led ourselves," says the older Piper (Clive Geraghty); infected with cultural bloodlust, they wished for their deaths, but these do not occur before the realisation, in some of these men, that they owe their deepest allegiance not to king, country, or Ulster but to one another. They are what is worth fighting for, but they are powerless.

With its blood-red sky, grave-like trench, and insistent drum-beat that gives the play its ominous pulse, and it's charged positioning of sacred tribal objects on abare stage - the Lambeg drum, the Boa Island idol, the Bible on a lectern etc - the production has a rinsed, uncluttered, almost abstract feel that marvellously suits the poetic purity of purpose in this, the finest Irish anti-war play since Silver Tassie.

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