Way To Heaven, Royal Court Theatre Upstairs, London

"May I ask: have you any experience of the theatre?" the Nazi commandant asks Gershom Gottfried, the inmate he's chosen to be a sort of liaison officer with the other Jewish prisoners. It's 1942 and this is a concentration camp, but the commandant is intent on staging a macabre, perverted foray into theatrical illusion.

Way to Heaven, a compelling, cunningly constructed play by the Spanish dramatist Juan Mayorga, begins at the end. The audience sit like a class on the floor while the English Red Cross representative (Jeff Rawle) delivers his troubled narrative of the day in 1942 when he visited the camp, on the pretext of offering medical supplies, and was given a tour.

It's easy to see now that he should have blown the whistle. The station still smelt of paint. The square, the park, the orchestra stand - it all had the unreal feel of a toy town. The children on the swings and the old folk enjoying the sunshine had the air of people awkwardly playing parts. Today, standing in this place, now overgrown with woods, the Englishman feels horror and self-recrimination, but maintains that he would have told the truth if Gottfried, the supposed mayor, had given him a clear sign.

Arrestingly staged in semi-promenade fashion by Ramin Gray, the piece then offers us vignettes of what we gradually realise must be rehearsals of slices of "authentic" camp life. Boys wearing yellow stars row over spinning tops or ask prurient questions about their sisters. The dialogue is stilted. There's an oppressive sense of being watched. The most spontaneous gesture in these scenes is when the young woman in a courting couple accidentally drops a package on hearing the noise of one of the trains, whose purpose is still an unnerving mystery to them.

Then the play takes us "behind the scenes", as it were, of this colossal charade. Dominic Rowan's Spinoza-quoting, creepily culture-buff commandant is like a parody of an over-controlling theatre director as he moves tiny figures round a model of the town and brings the wisdom of Pascal, Aristotle et al to bear on his stupendously phoney project. We see how he saps the will to protest of Gott-fried (played with a terrific power of contained reproach by Richard Katz) with implied threats (as long as they are here, they are not on the train) and debilitating speculation.

There's a crucial moment, though, after the Red Cross man has gone. In a fit of post-show melancholy, the commandant admits that he almost wished Gott-fried had rebelled as a relief from the suffocatingly micro-managed spectacle. It's as though, in ways that will later be denied, this project has alerted him to the megalomaniac control-freakery of Nazism in general and the lack of anything genuine behind it. Way to Heaven shows us how good theatre can nail down the symbolic and immoral emptiness of bad.

To 9 July (020-7565 5000)