THEATRE; Einstein's theory of relationships

Terry Johnson's Insignificance is a chemical experiment written up in dialogue. The premise throws two 20th-century icons, a dumb blonde actress and a brainy, grey professor, into the confined space of a hotel room in Manhattan, and observes how opposites attract. It turns out she's keen on his physics, and he's not averse to her physique.

To test the strength of their mutual adhesion, two more bodies are pitched into the crucible, a ball player and a senator, each of them intent on pulling the pair apart. The result of the experiment is a large, invigorating atomic explosion. This is presumably proof that the mind and the body should have nothing to do with each other, but also doubles as a reveille to any intellectual stragglers in the house exhausted by Johnson's sometimes remorseless play of ideas.

Even site unseen, it says a great deal for this Donmar revival that it tempted its two principal stars back to the stage after a long absence. Frances Barber would have been drawn by the irony built into the idea of Marilyn Monroe, wearing the flapping white dress that billowed around her ears in The Seven Year Itch, as a great stage role.

Barber has the mannerisms off pat, but clearly doesn't share her character's enthusiasm for the theory of relativity. There's something clogged and weary in this core phase of the play, alleviated only when Barber, after demonstrating the theory, lies slumped on the bed as if in post-coital ecstacy: "Vood you like a cigarette?" enquires Alun Armstrong's hunched, shuffling Einstein.

Armstrong attempts, and pulls off, a subtler piece of scene-stealing than anything written for the actress. He portrays the man famous for measuring energy, but like the nucleus of an atom Johnson's direction leaves him all but static while the more proactive characters whirr around him, fighting, divorcing, having miscarriages and causing mini bubble- gum explosions. Armstrong can scarcely have moved so little on a stage, and yet you can't take your eyes off him.

The play itself has been away for a while too. Notwithstanding Nic Roeg's 1985 movie version, it hasn't been seen on stage since it first surfaced in 1982, and requires several strikes of the match to ignite. Ian Hogg, as the thuggish senator who cannot persuade the professor to testify to the House of UnAmerican Activities, never quite wins his battle with McCarthy's slippery southern drawl. As Joe DiMaggio, Monroe's ball-playing dolt of a husband who fails to entice her home, Jack Klaff convinces with a bawling Brooklyn accent. The whole show works better when relations, rather than relativity, are the focus, which conclusively proves that theory isn't a patch on practice.

n Booking to 6 August (Box-office: 0171-369 1732)