'EVERYBODY in there either has a death wish or criminal intentions': that's a pretty widely applicable description, capable of embracing everything from Strangeways to the Royal Academy Summer Exhibition. In this instance, though, it refers to a municipal swimming-pool in Hounslow, the setting for a number of scenes in Jane Coles' new play Backstroke in a Crowded Pool. Here we watch two young attendants - Lynsey (Tracy Keating) and Chrissie (Sophie Stanton) - as they chatter to one another and keep a sharp whistle trained on the massed malefactors (heavy petters, sawn-off-denim wearers, plaster- losers, etc) thrashing about in the water.

A poolside perspective could give a person a jaundiced view of the human race, but it also, we gather, provides an excellent view of the sexual talent and a decent supply of metaphors for more metaphysical matters. The charmed life of the woman who serenely backstrokes up and down the choked pool, heedless of the people who obligingly get out of her way, is a symbol, for Lynsey, of God's solicitude for his creation. That is, until the woman virtually drowns one day . . .

There have been stage plays set in Turkish baths (Nell Dunn's Steaming) and in saunas (Iain Heggie's A Wholly Healthy Glasgow), but I can't recall another work that takes the mainstream plunge in this way. And with her dreams of getting a job on a liner (all that lovely unchlorinated, Elastoplast-free water) and her wised-up patter about stress, Chrissie, the would-be masseuse / beautician / reflexologist, is a delightfully observed (and acted) creation.

It might seem a largeish jump from this milieu to the world of animal rights activism and of arranged marriages. It turns out, though, that Lynsey has fallen in love with Hashim (Raji James), a young Muslim boy, and has converted to his faith. Carol, her mother, is an animal liberationist and is spotted on a video putting a brick through the window of a halal butcher's. Mindful of the way right-wing groups have used animal rights as a pretext for racism, Hashim storms out, claiming that Carol is no better than the louts who recently held a knife to his mother's throat.

These are interesting clashes, but they are written up in a rather wooden manner. The whole life versus the right-to-kill theme is too diagramatic: Chrissie rounds off the play with a conveniently life-affirming suspected pregnancy just after Lynsey's revelation that, for the animals' cause, she has murdered a man and his child. Coles does not pass judgement on any of the views expressed, but there's a difference surely, between not editorialising and seeming impartial to the point of vacuity.

The best parts of the play, and those which give John Dove's production its strong charm, are the many moments of digressive, quirky humour. At one point, Hashim's delightfully talkative mother (excellent Leena Dhingra) orders him to freeze-frame the smuggled animal rights video. Ignoring the violence on the halal butcher's, she draws excited attention to the blouse in the neighbouring shop window. Why, it's the one she's now wearing] It's at such moments - of inconsequential humour rather than earnest theme-furthering - that Backstroke leaves the shallow end.

'Backstroke in a Crowded Pool' continues at the Bush, Shepherds Bush Green, London W12 (Box office: 081-743 3388).