Theatre / THE STEWARD OF CHRISTENDOM - Royal Court, London

Sebastian Barry wrote The Steward of Christendom as a way of discovering and coming to terms with his great-grandfather, Thomas Dunne - the last Catholic head of the Dublin Metropolitan Police before Irish Independence in 1922, a loyal servant of the British and hence not, as Barry writes in the programme, a comfortable ancestor.

However uncomfortable he may be with Dunne's legacy, though, Barry has managed to create a wonderfully compassionate picture of the man. The play - originally produced at the Royal Court Theatre Upstairs earlier in the year and now transferred to the main stage - finds Dunne in the last years of his life, confined to the county home at Baltinglass, County Wicklow, where he drifts randomly between an undignified, spartan present and the past - the pastoral idyll of his childhood; his father's harshness towards him; the pride he took in his work as a policeman; the death of his wife in childbirth, and of his only son in the trenches; and his estrangement from his three daughters (the echo of "Lear" seems deliberate).

Barry writes with an eloquence that makes the play constantly fascinating and moving, but I still have two major reservations. The first is that, while it's clearly part of his purpose to show the way that public life reflects and magnifies private life, the connections he draws are at times crude and unconvincing, and he often seems to assert rather than dramatise them. In one speech, for instance, Dunne talks about the fierceness of his love for Queen Victoria, implying that the happy home life of our own dear Queen in some way guaranteed political stability: "Ireland was hers for eternity, order was everywhere, if we could but honour her example. She loved her Prince. I loved my wife." That there was a political dimension to royal domestic arrangements is undeniable; but here the link seems unconvincingly straightforward, and Dunne's frank worship nothing like as plausible as the mocking, half-resentful loyalty to "the Widow of Windsor" that Kipling portrayed.

The second reservation is about the structure of the play: darting back and forth between past and present, between the seen and the imagined, it has little momentum. The last scene of the play, for instance, is the day that Dunne loses his wits from the way this has been set up in advance, with Dunne dropping hints about "that last day with Annie", you feel this ought to be some kind of climax or revelation; but what actually takes place fits seamlessly with what you already know. The fact is, you feel that you could lose 20 minutes from the play's two and a half hours at almost any point without changing its overall impact.

The play's faults are blurred by Max Stafford-Clark's excellent production, and by Donal McCann's superb central performance. McCann shows us Dunne visibly struggling between the need to remember and the urge to forget his past life, trying to reconcile his love of his children with his treatment of them, and his love of his country with the contempt his countrymen feel for him. This is virtuoso acting, but the technique never detracts from the immense emotional power; and it's worth the price of admission on its own.

n To 7 Oct. Booking: 0171-730 1745