Andorra, Young Vic, London

The casting in Gregory Thompson's impressive production of Andorra is blind to colour and to disability. There's nothing outré or self-congratulatory about this policy as deployed here: rather, it makes its own tellingly defiant statement, given that Max Frisch's 1961 play – which explores the mechanism of racism – is an eloquent, despairing study of man's compulsion to stereotype and scapegoat.

The people of Andorra are living in dread of attack from their anti-Semitic neighbours, the Blacks. Their anxiety begins to affect their attitude to Andri, the Jewish foster son of Can, the local schoolteacher (a fine, drunkenly despairing Jack Shepherd), who allegedly saved him by smuggling him as a baby across the frontier. Now, for example, the carpenter, who was already demanding an extortionate price to apprentice the youth, finds a blatantly dishonourable excuse to renege on the deal. He fails Andri by criticising and dismantling a rubbishy chair actually made by one of his own employees.

At the back of the sultry town square on Francis O'Connor's handsome set, the inhabitants (doctor, innkeeper, soldier, priest etc) sit stacked in their homes like ominously watchful specimens in a cabinet. Aided by Paule Constable's superb lighting scheme, it's a design that allows great ease of contact with the audience – useful for a play that keeps interrupting its present-tense action with flash-forwards to the townsfolk's attempts at self-justification after the tragedy.

Thompson has dispensed with Frisch's over-literal device of having the folk enter a witness box at such moments. Instead, his excellent cast fluently weave between the ongoing drama and their post hoc, direct-to-audience wheedlings. The effect is desperately depressing. Even before the horror occurs, we know that almost no one will learn anything from it or accept responsibility.

Because of the temporal shifts, the play's central irony becomes apparent early on. Andri, the target of the Andorrans' growing anti-Semitism, is not in fact a Jew but the schoolteacher's illegitimate son by a foreigner. The act of courage was bogus and based on moral cowardice. So, there's a gruesome comedy in those scenes in which the townsfolk identify Semitic characteristics in Andri and twist everything he does to corroborate their prejudices. "Did anyone ever meet a Jew who could take a joke?" asks Morris Perry's insufferably silky and complacent doctor when the youth unaccountably fails to be tickled by a volley of racist abuse.

Alec Newman makes a powerful, emotionally transparent Andri, journeying from a winning, open-hearted optimism, through the false security of hatred, to a kind of heroic fatalism when he refuses to capitalise on the revelation that he is not Jewish.

On the evidence, though, of Andorra and The Fire Raisers (the other Frisch play performed in England), there's nothing wrong with this dramatist's work that could not be put right by lavish use of a blue pencil. Even a production as involving and stealthily measured as this cannot disguise the heavy-handed protractedness of the proceedings or the frequent waiting while the play laboriously catches up with your intuitions. "How slow. How slow they are," Andri complains, about the tardiness of the troops coming to seize him. It's a charge you could level at the pace at which points are made in this pregnant but rather pedestrian political parable.

To 10 Nov, 020-7928 6363