Mappa Mundi, NT Cottesloe, London

When all's said and done

Shelagh Stephenson had a hit a few years ago with The Memory of Water, a searingly funny piece about the social stresses of bereavement and the inescapable power of the past. It's the pain and family friction caused by terminal illness that is the focus of her new play, Mappa Mundi, premiered now in Bill Alexander's over-reassuring production at the Cottesloe.

The central character is Jack, a seventysomething Northerner with only three months to live. This former bookkeeper and keen amateur map-collector sits in a walled English garden (the picturesque set is by Ruari Murchison) and reflects on the difference between the comforting precision of cartography and his increasing sense of the failure and formlessness of his own life. The garden belongs to his daughter Anna (Lia Williams), who, in too neat a counterpoint to her father's contemplation of dying, is engaged in preparations for her wedding to Sholto (Patrick Robinson), a black fellow-lawyer.

Jack's research of the family tree indicates that their ancestors may well include a genuine black slave as well as the authenticated white plantation-owner. Anna embarrassingly believes that this gives her a deeper bond with her fiancé – a suggestion that Sholto curtly dismisses, telling her, "All that matters is how you are now." It's hard to believe that a woman of Anna's education would be guilty of such romantic naivety. But then, for the purposes of the play, she has to perpetrate a more painful solecism.

She and her brother Michael (Tim McInnerny), a struggling middle-aged actor who still longs for his father's approval, have had a special aerial map of his life made for Jack. Short of presenting him with a wall-chart for crossing off the days till his demise, it's hard to see how they could have done anything more woundingly tactless. For the ambit the map traces is depressingly narrow and localised. "I thought my life would look like more than that," is his response, as he kneels, in tears, on its surface.

Replacing an indisposed Ian Holm, Alun Armstrong makes Jack's ordinariness compelling in a performance of magnificent restraint and quiet humanity. He conveys both the cussed curmudgeon who can't resist using the C-word in the company of James Hayes's rum Catholic priest, and the autodidact bookkeeper who tots up his life with a nonplussed anguish, and finds that he: "Married one wife, fathered two children who are now adult strangers. And that's it. Finished."

Mappa Mundi is often funny, moving and acute in its depiction of what can and cannot be communicated in the last days of one's life. But as with Simon Russell Beale in Humble Boy, another Cottesloe comedy set in a fetching garden, I felt that the central performance was better than the magpie-minded play.

Too many elements fail to emerge naturally from the basic situation. Ideas and metaphors are dragged in and left undeveloped. For example, Jack is conveniently lent a book on quantum physics that allows some forced chat about Schrödinger's cat and musings about parallel universes: "A me who made different choices." And when, in the second act, he lets the skeleton fall out of his cupboard, you'd swear it was a plastic fake – for the crime to which he confesses seems as contrived to suit Stephenson's thematic design as the energetic multicultural dancing display that brings the piece to a somewhat hollowly harmonious close. For a play that deals with such primal emotions, Mappa Mundi leaves you feeling oddly disengaged.

To 29 Nov (020-7452 3000)