Cosí fan Tutte, Garsington Opera Garsington

Irving Berin unwittingly provided the best of all plot summaries for Mozart's Cosí fan Tutte: "Lord help the mister that comes between me and my sister and Lord help the sister that comes between me and my man". Perfect. As is the opera. But like all the best comedy-dramas its durability lies in keeping some home truths credible for a sceptical modern audience. At Garsington, John Cox has come up with one of the simplest and smartest solutions yet to the credibility of Lorenzo da Ponte's plotting.

Irving Berin unwittingly provided the best of all plot summaries for Mozart's Cosí fan Tutte: "Lord help the mister that comes between me and my sister and Lord help the sister that comes between me and my man". Perfect. As is the opera. But like all the best comedy-dramas its durability lies in keeping some home truths credible for a sceptical modern audience. At Garsington, John Cox has come up with one of the simplest and smartest solutions yet to the credibility of Lorenzo da Ponte's plotting.

Cox's setting (designed by Robert Perdziola) is a smart spa hotel. Don Alfonso is the manager, and like all good hotel managers he's a manipulator. Now, as we know all too well, he makes a wager with Ferrando and Guglielmo to test the fidelity of their fiancées, the sisters Dorabella and Fiordiligi, and it hinges on the pretence of their menfolk being sent away to "the field of battle". Cox updates the play to the Great War and thus instantly gives the drama a cruel edge. While men in their tens of thousands are being called-up to fight - Ferrando and Guglielmo merely pretend, leaving their fiancées believing in their plight. It's very clever, and the pay-off is chilling and poetic.

Cox uses Garsington's courtyard stage most effectively. At one point, he sets up a poignant juxtaposition with Dorabella and Fiordiligi pining for their lovers in one room while the chambermaids do likewise in another. And Cox seizes a brilliant comedy opportunity as the sisters become nursing auxiliaries just in time for the scene where the lovesick "strangers" feign death-by-poison and Fiordiligi is seen frantically consulting her handbook.

The young cast are in the main splendid though they could all learn from Lillian Watson's Despina. Her experience and charm oozes from every pore as the opportunistic maid inveigles herself into our confidence. Sarah-Jane Davies (Fiordiligi) is currently studying with Watson, so she'll be picking up pointers. It's a smashing voice and she steered it through the treacherous peaks and troughs of her two arias with real aplomb. I'd have pruned away some of the ornamentation in "Per pieta", if only because the starkness of what Mozart actually wrote, while cruelly exposed, is more deeply affecting. But it's a lovely performance, and well complemented by the feisty Dorabella of Wendy Dawn Thompson, also a promising singer.

So, too, Edgaras Montvidas as Ferrando. His sensitivity in "Un'aura amorosa" was marred only by too much pressure at the top of the voice, which is something that the lack of a helpful acoustic at Garsington exposes. Daniel Belcher's (Guglielmo) problem is that he needs to sing out more. By Act II, he was doing just that. Steuart Bedford kept his band in check from the harpsichord. Jane Fenton (cello) his able continuo partner.

And that chilling twist at the close? Stop reading now if you have tickets. But history has a habit of repeating itself. The chaps are called-up. Only this time it's for real.

The production is at the Barbican, London EC2 (020-7638 8891; www.barbican.org,uk), on 17 July