Tony Harrison's Fram is long and mind-knottingly complex, but it is neither self-indulgent nor superfluous. It is one of the most stimulating, engaging and extraordinary evenings on offer. Its message is simple: it asks what role the arts can play in a world where illegal immigrants fall from their hiding places in the wheel bays of aircraft, and four-year-olds starve to death in the Russian famine. So the beautiful ballet that Viviana Durante dances and that so many critics have complained about has to be performed in its entirety, juxtaposed as it is against the gritty realism of starving Russian children. The frills of a verse drama are necessary in the same way: the play needs a lack of realism, it needs to be elaborate in the way that the ballet is elaborate, to question its place in the world. The layers at work are extraordinary: we are constantly made aware that we are in the National Theatre watching actors playing actors putting on a play watching a play.
Of course, the arts are vital, as this play makes blisteringly clear. Sian Thomas's speech of Sybil Thorndike's, four pages of rhyming couplets evoking a starving Volga woman's cannibalism, has been described as the only good moment in the play. But she is extraordinary here (vomiting up food eaten too fast, before flicking out of character and apologising that she wasn't really starving) and in a speech at the end, portraying a B&Q worker who finds an immigrant who has fallen, frozen and frightened, from an aircraft. Mark Addy and Jasper Britton are superb too, as the polar explorers, the hooks that Harrison hangs his themes on, since Fridtjof Nansen was involved in the first efforts to make people aware of the Russian famine and to provide passports for immigrants.
At the end, a Kurdish poet, whose eyes and mouth have been sewn up, limps through Westminster Abbey. Harrison uses elaborate poetry to tell us that the only poetry able to describe the world's atrocities is silence.
Bob Crowley's set design, incidentally, is beautiful: the omnipresent ice, the awesome model of the ship Fram itself and the clever and telling video projections of the National covered in ice.
Fram is complicated, but it fits together under the exquisitely rhymed poetry and Harrison's direction. And it succeeds in creating one of those evenings of drama that manages, as Tom Stoppard wrote, to "nudge the world a little", to make you consider the world afresh.
To 22 May (020-7452 3000)
Oliver Soden, student, Henfield, West Sussex