Tom Stoppard has done many odd, adventurous things in his career, such as transforming university philosophers into yellow-suited acrobats, but he's done nothing more gloriously preposterous than bring on stage a whole orchestra, primarily to embody the sounds in a Russian schizophrenic's brain. But expense isn't the only reason that his 50-minute Every Good Boy has resisted revival since its premiere in 1977. Its subject feels dated. Stoppard's target was the Soviet Union's maltreatment of dissidents and, though Russian troublemakers have developed a habit of being killed, the State is less likely now to trap them in mental hospitals. Or is it? Might that, could that, will that sometimes still be their fate? Ask Roman Nikolaichik, sent to an asylum last year after canvassing for Other Russia.

Certainly, Felix Barrett and Tom Morris's production is ominously alive. Richly alive, too, thanks to the presence of 40 members of the Southbank Sinfonia. Their task is to play André Previn's score: which can be loud and dissonant, mainly when Toby Jones's podgily nerdish yet scarily erratic Ivanov is hallucinating their presence, but can also be soft and grave, mainly when Joseph Millson, who is also called Ivanov, is describing the deprivations and tortures he suffered after making a mild political protest.

Both men share a two-bed ward, or cell, at the front of the stage. The obsessive Jones has the Stoppardian lines, wildly talking of drummers with whom he's “shared a plate of tagliatelli Verdi and stuffed Puccini” and so on. Millson isn't funny at all, since he resolutely refuses to accept his doctor's cheery diagnosis, which is that “your symptoms are your opinions, your disease is dissent”, and goes on hunger strike to the dismay of Bryony Hannah as his baffled, touching son.

The problem in 1977 was that, despite its witty connections and wonderfully ironic resolution, Every Good Boy was actually two plays not so seamlessly forced into one. But the directors have had an idea that brilliantly links the lunatic's and the dissident's stories. Suddenly, thuggish warders patrol the orchestra, seizing, beating, even killing players in a crazed ballet, which emphasises that both men inhabit the same mad, unjust world.

Moreover the ending, which could seem sentimental, isn't at all. I won't reveal the details, just say that Millson hardly reacts when Hannah reaches towards him. He sits motionless in his wheelchair, a wizened figure staring intensely ahead and leaving me, for one, to wonder what time and place is riveting him. A future Russia? A future world? This superb revival leaves you hoping not but fearing so.

Box office: 020-7452 3000, to Feb 25

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