Mammals, The Bush, London

One of the most striking moments in Amelia Bullmore's sharp domestic comedy comes early on when Kev, the devoted husband and father whose work keeps him away all week, returns home early and falls into a hug with his wife, Jane.

One of the most striking moments in Amelia Bullmore's sharp domestic comedy comes early on when Kev, the devoted husband and father whose work keeps him away all week, returns home early and falls into a hug with his wife, Jane. I can't remember having seen in the theatre an embrace like the one Daniel Ryan and Niamh Cusack manage here: meaty, unreserved, a couple wrapped together without any sense of risk or flirtation. They capture perfectly both the intensity and the familiarity of their affection; and, watching them, I realised how rare it is for theatre to offer an authentic representation of bourgeois domestic happiness.

It can't last, of course. Jane, stuck at home with the kids, is more frustrated than Kev can realise; and he has returned early to make a confession: he is in love with a colleague. Before they can begin to understand where this leaves them, Kev's best friend Phil turns up for the weekend, with his high-maintenance girlfriend, Lorna: they, too, have their troubles. The emotional permutations are played out as farce, the couples fitting in crises between social duties, interrupted by Kev and Jane's children, four-year-old Betty and six-year-old Jess, who fire off appallingly frank questions about death and sex.

Bullmore has written a good deal for television, and it shows in her ear for dialogue and her dead-on observation of domestic minutiae. In particular, she captures the underlying brutality of parenthood, where love isn't necessarily underwritten by conscience on either side, and deceit is just a necessary management tool. The authenticity is well served by Anna Mackmin's attentive direction and Paul Wills's set, in which economical good taste is littered with the wrack of soft toys, felt-tips and plastic bricks. During the opening scene, in which Jane struggles to herd her offspring through breakfast and off to school, I winced repeatedly in recognition - the children's unscrupulousness in argument ("Do you want me to poo in my pants?"); the rapid untangling of parental patience: ouch.

But Bullmore doesn't fall into the trap of offering TV-style authenticity. Realism is disrupted by having adults play the children. To begin with, it has a forceful logic - the children loom up against Jane, giving immediate physical expression to her sense of being overwhelmed. As the play progresses, it is used for comic - often hilarious - effect. Helena Lymbery and Jane Hazlegrove rarely let childish mannerism tip over into caricature, so that there is room for tenderness.

The play has flaws and frustrations. The plot is overreliant on coincidence and a contrived 11th-hour catastrophe; Phil and, especially, Lorna are underwritten (though Mark Bonnar's and Nancy Carroll's performances are, like all the others, droll and committed). But for the most part, Mammals is a clever, funny debut, and painful in all the right ways.

To 7 May (020-7610 4224)