Mercy, Soho Theatre, London

Lin Coghlan's new play, Mercy, reminds me, in one crucial respect, of The Mercy Seat, the last theatre piece by Neil LaBute, though its spirit could scarcely be more distinct.

Lin Coghlan's new play, Mercy, reminds me, in one crucial respect, of The Mercy Seat, the last theatre piece by Neil LaBute, though its spirit could scarcely be more distinct. In the American drama, a thirtysomething New York executive, married with children, decides to capitalise on the catastrophe of the twin towers and on the fact of his presumed death by heading off into a brand new life with his mistress. LaBute's handling of the material was so cynical, however, that it left him in much the same position as his anti-hero - unable to avoid the charge of cold-hearted exploitation.

There are characters in Coghlan's play who also yearn to take advantage of disaster by assuming new identities. The difference is that these teenagers are in genuinely desperate straits. There's no luxury here of hovering like a spoilt consumers over lifestyle alternatives. Graduates of a London sink estate and a young offenders' unit, Deccy and Mac, who has his backward brother in tow, are on the run from a rival gang. A cocky army cadet, Terry, has abducted the 15-year-old Jean from a residential home. Having got plastered and then mugged after absconding from his marriage, even Mac's troubled social worker - a man not averse to buying drugs from his young clients - hoves into view.

An apocalyptic storm rages. The descent of a white powdery substance leads to the mistaken belief that London has suffered a chemical weapons attack. A sea-wall collapses and the flood level is rising dangerously. By dint of some wildly improbable coincidences, these various characters converge on a barn in Kent that provides shelter like the hovel in King Lear. The set-up of beleaguered isolation may be awkwardly established (the total absence of mobile phones takes some cumbrous explaining) and there are baffling and bizarre symbols (there can't be many barns where you'd find a sack full of dead monkeys). But instead of feeling inflated and melodramatic, the extremity of the situation is used to point up how, for these people - with their lives blighted by domestic violence, poverty, drugs, and abusive fostering - the world is a constant cataclysm.

Mercy calls to mind Edward Bond's and Sarah Kane's Blasted. There's a similar sense of staring into ultimate bleakness and not giving up on the human spirit. Coghlan's approach is more sanguine, however.

Cared for with compassion by Jean, the baby found in a ditch here suffers a happier fate than the equivalents in Bond and Kane who are, respectively, stoned to death and eaten. But it's significant that Mercy also shows how the awful Terry uses the baby and Jean as a passport to escape. Because of qualifying details like that, you respect all the more how much the play rescues from the flood-tide of fashionable pessimism.

To 7 August (020-7478 0100)