The Little Dog Laughed, Garrick Theatre, London

To describe the handsome Rupert Friend as Keira Knightley's current squeeze may sound a touch disrespectful, rather as if one were to refer to Simone de Beauvoir, say, as Jean-Paul Sartre's arm-candy.

But that's what he is, lucky guy, and here he is making his high-profile professional stage debut as one of the leads in Douglas Carter Beane's bouncy Broadway comedy The Little Dog Laughed. At least Keira will know where he is in the evenings while, a few streets away, she is breaking her own theatrical duck in style in The Misanthrope.

Nor does she need to worry that female love-interest onstage will turn into an offstage romance, for her beau is playing Mitchell, a dashing boy-next-door type actor and aspiring movie star, whose professional secret is that he is gay. And in the course of the proceedings, our hero falls in love with a male prostitute who hitherto had always thought of himself as a straight guy servicing other guys merely in order to pay the rent. Indeed, the reluctant male hustler (played with a winning sensitivity by Harry Lloyd) occasionally sleeps with a lovelorn – and underwritten – female friend, portrayed here as a nice mix of the ditzy and the distressed by Gemma Arterton.

The character who powers the evening forward, though, in Jamie Lloyd's enjoyably breezy and knowing production, is Diane, Mitchell's diabolically cynical lesbian agent. She makes the average monstre sacré look like a fluffy kitten in a cat food advert. And in a performance of brilliantly malign energy, Tamsin Greig shows you a woman who has a well-thumbed movie-industry directory where her heart should be. "Are you British? Do you have a knighthood? Then shut up!" she bawls at her client Mitchell, whom she wants to keep firmly in the closet.

The scenes that attempt emotional seriousness, though, ring hollow. The thin characterisation of the young girl suggests that the author is much less interested in straight, sincere females than he is in dyke divas. And there seems far less at stake here than in, say, Take Me Out, the American play at the Donmar a few years back about the exposure of a gay baseball superstar. But the production has a lot of diagrammatic pep and Greig is phenomenal as corrupt Hollywood ambition incarnate.

To 10 April (0844 579 1974)