The Overwhelming, Cottesloe, NT, London<img src="" height="1" width="1"/><img src="" height="10" width="47"/>

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The Rwandan genocide, in which an estimated 800,000 people were slaughtered, is the theme of two recent films - Hotel Rwanda and Shooting Dogs. But The Overwhelming, the powerful new play by J T Rogers, is, to the best of my knowledge, the first stage treatment of the subject. It is set in early 1994 as tension mounts between the majority Hutu population and the minority Tutsis. We see the build-up to disaster, the intractability of the hostilities in Rwanda, and the indifference of outsiders from a newly arrived US family's perspective.

Jack (Matthew Marsh), an academic, is writing a book on activism and wants to focus on an old Rwandan college friend, Joseph (Jude Akuwudike), a Tutsi who now runs a children's HIV clinic in Kigali. Invited by Joseph, he travels to Rwanda, taking his wife (Tanya Moodie) and his estranged 17- year-old son (Andrew Garfield), who has just lost his mother.

But when they arrive, Joseph has vanished. While Jack makes enemies by investigating his disappearance, his son enjoys a sexual initiation in Kigali and the wife, researching for a book of her own, comes under the spell of a persuasive, deceptively friendly Hutu "patriot" (Danny Sapani).

Premiered in Max Stafford-Clark's immaculate and engrossing co-production between the National and Out of Joint, the play, to some effect, places the audience in the same position as the newcomers - out of its depth in a society where there has been a complete breakdown of trust. There's a fine narrative stealth in the gradual way Rogers exposes the scale of the mutual animosity and a terrible pathos in the excerpts from an earlier hopeful letter from Joseph.

As he's supposed to be a specialist in international relations, it's hard to credit the degree of Jack's initial pontificating naivety. But his political awakening - in biting scenes with obstructive police chiefs ("Hutu do not get Aids. Aids is a Tutsi sickness") and UN Majors, NGOs, embassy officials and other "realists" all resigned to not intervening - is arrestingly dramatised. The play refuses to introduce any false sense of redemption. Though it has flaws, it fulfils Shelley's words - that art should help us "to imagine what we know" - and offers a rousing rebuke to indifference.

To 8 August (020-7304 4000)