The Vertical Hour, Royal Court, London

Haunting display of the pain of war

David Hare's The Vertical Hour is that rare bird: a new play by a British dramatist that began life on Broadway rather than in London. The piece itself has a foot in the US and in England. Book-ended by scenes at Yale University, the play takes its female protagonist – a professor of international relations who, in her former career as a war correspondent, had seen action in Bosnia – on a trip to the Welsh border country. Here her values and moral sensibility collide with those of her English boyfriend's father. Once a fatal womaniser, this doctor is now a kind of reclusive Shropshire cad, or rather ex-cad.

So a Broadway opening, directed by Sam Mendes in November 2006 with American film star Julianne Moore as the lead, had a certain symbolic appropriateness. The trouble, though, was that Moore was miscast, coming across more as an agonised mature student than an outwardly forceful professor and Bill Nighy, demonstrating his trademark tics as though he were being paid on some quota system, wiped the floor with her in debate. Indira Varma and Anton Lesser are much more evenly matched now in Jeremy Herrin's beautifully nuanced and well-paced UK premiere at the Royal Court.

Under the artistic directorship of Dominic Cooke, this famously left-wing and oppositional theatre has begun to subject liberalism to searching scrutiny. Last summer, the lip-service idealism of well-heeled, soi-disant American liberals was satirically excoriated in The Pain and the Itch. Now, through the high-minded scorn of Nadia, the Yale professor who backed the invasion of Iraq as a humanitarian crusade and even briefed Bush, the kind of self-hating liberal who champions the right of others to hate the West ("If I were them, I'd hate us too") is examined and challenged.

The success of the evening is largely due to Varma's superb performance. Projecting both the combative humour and the emotional confusion of this feisty young woman, she makes the character's contradictions feel complex rather than (as Moore did) clunkingly inconsistent.

Nadia is a temperamental cousin of Susan Traherne, the Resistance heroine whose frustrated idealism turns destructive during the compromises of the post-war years in Hare's Plenty. The difference, as Varma vividly delineates, is that Nadia is consciously torn between distrusting her own addiction to angry self-righteousness and an absolutist desire to break loose from pampered, materialistic modernity that betokens (in ways that Hare under-explores) certain temperamental affinities with Islam. When the doctor, quoting from Henry V, argues that "The West's been using Islam as a useful enemy for as long as anyone can remember", it feels like a dramaturgical cop-out that she fails to respond.

I never believed that Nadia would have looked twice, still less embarked on a relationship with Tom Riley's cipher of a physical therapist. Nor is it easy to credit that Nadia can have seen at first hand the terrible consequences of the invasion of Iraq and still resist acknowledging that the intentions of the invaders helped to shape those consequences.

In the first half, Lesser's lack of seductive sex appeal as the doctor with the guilty past lowers the charged edginess of his encounters with Nadia. But Herrin's production builds up by stealth an intensely absorbing atmosphere of mutually revealed pain in the long al fresco sequence where the two of them talk and drink until dawn and shock each other into self-knowledge. All of the characters are in flight from their haunted inner lives.

The Vertical Hour shows that it's deluded and damaging to suppose that you can set aside personal agonies and equally harmful to view the outside world as a projection of private passions. So how do you relate the inner to the outer? This difficult question that animates a play that is sometimes schematic but which, as sensitively and subtly realised here, will continue to nag the mind long afterwards.

To 1 March (020-7565 5000)