'Statira was a rather naïve character," conductor Laurence Cummings informed us as he described the Emperor's daughter in the Vivaldi opera L'incoronazione di Dario. This turned out to be a considerable understatement, for it transpired that Statira has already agreed to marry two suitors before taking on a third. "Why is he so cross?" she wonders as suitor number three gets understandably nervous.

L'incoronazione receives its UK premiere at Garsington Opera this summer, and here Renata Pokupic (pictured) provided a tantalising preview of her forthcoming performance as Statira - tantalising for those lucky enough to be going to the opera itself, downright frustrating for everyone else.

Pokupic has a voice, and a cheeky grin, that can be described in one word: ravishing. She also has a very impressive vocal range, and an ability to instantly switch mood, as she demonstrated in her next aria, the sublime and yearning Erbarme dich from Bach's St Matthew Passion. Here her voice combined beautifully with Eleanor Harrison's solo violin. Later, she proved that she can also pack a considerable punch, in two arias from Handel's Ariodante. Quite plainly, Renata Pokupic is a class singer.

Pokupic was accompanied by the Royal Academy of Music Baroque Orchestra, a band of top students playing period instruments (or modern copies) from the academy's collection. Gut strings are used, and these inevitably produced a few tuning challenges in Garsington Great Barn's rather moist atmosphere. In Vivaldi's Concerto for four violins (RV580), for instance, the four soloists didn't always quite blend with each other, and I suspect this wasn't entirely due to differences in the pedigree of their instruments. Already true professionals, however, they produced a warm, feather-light performance - a pity the players concerned weren't identified in the programme.

Less successful was Bach's Concerto for Harpsichord (BWV1055), where the orchestra needed to bend over backwards not to swamp soloist Laurence Cummings. Sitting towards the back of the hall, the result was that the accompaniment sometimes disappeared altogether. Everyone was robustly audible, however, in the final work, Handel's Concerto Grosso Op 6 No 11.

Llyr Williams (piano) gives the second Garsington Spring Concert on Monday. Tickets: 01865 361636.