Mostly Mozart: Zaide, Barbican Centre, London <!-- none onestar twostar fourstar fivestar -->

It's official, then. Mozart was a passionate activist for the anti-slavery movement. And even if he wasn't, he now is. That most compassionate but sometimes misguided of directors, Peter Sellars, has recruited him to the cause. Agencies for the eradication of human trafficking and slavery greeted us upon entry; on-stage speeches were made. All because Mozart, aged 23, wrote an unfinished singspiel called Zaide.

There's no question that Zaide addressed the issue of slavery (not uncommon at the time - this was a social reality), that it furthermore touched upon the Christian/ Muslim divide. But to characterise it now as a conscious protest, a courageous indictment of human rights abuse, may be stretching hindsight just a little. No one begrudged the speeches. Art needs contemporary relevance. But hadn't Sellars loaded the dice?

For one thing, very little of Zaide remains - none of the dialogue, for instance. For another, Sellars chose to harness Mozart's fiercely reactive theatre music for Thamos, King of Egypt (written at the same time) to underscore a melodrama of his own. Effective, perhaps, in making a more dramatic case for Zaide but hardly a true representation of what Mozart wrote. Indeed, the pregnant pauses which now punctuate the "speechless" melodramas are turned to Sellars' advantage as "unanswered questions". Our generation must pick up where Mozart left off, he says, and provide some viable answers. Tell us something we don't know.

Still, the sincerity and intensity of this "concert staging" could not be doubted. Louis Langree and Concerto Köln helped load Sellars' dice with a blistering intensity. Like the show, the instrumental music was angry. On stage, the scene was set with the basic representations of a sweatshop. The male cast - to further underline the roots of slavery - was African American, the title role a Korean American. The point was well-made: equal and yet not.

Whatever you think of Sellars, he inspires optimum conviction from his performers. With Norman Shankle, Alfred Walker and Russell Thomas, it was the spirit more than the singing that moved. Hyunah Yu's Zaide caught well the ache inside. The lullaby "Ruhe sanft" dispensed enough compassion for the evening. Which was precisely the point.

Festival runs to 29 July