Ascanio In Alba, Barbican, London <!-- none onestar twostar threestar fivestar -->

It was to be expected (or hoped) that in Mozart's 250th anniversary year, stops would be pulled out. But four cheers to the Barbican for risking the opening night of its Mostly Mozart festival on an unknown opera by the 15-year-old not-yet-master.

What a revelatory evening! Here was Mozart, already a veteran opera composer with five shows under his belt, wrestling with a stock (and terrible) libretto in honour of the marriage of one of the Empress Maria Theresa's sons.

Ascanio in Alba, written in 1771, was Mozart's most important commission to date. This festa teatrale was to be the supporting act to an opera by Johann Adolph Hasse. But Mozart mightily upstaged his elder, leading him allegedly to remark, "This boy will cause us all to be forgotten."

No pain, no gain, is the moral of this tale - short and sweet but taking more than two-and-a-half hours. As is usual in these "pastoral" tales, gods intervene with demi-gods, nymphs, spirits, shepherds and shepherdesses. Here, Venus is arranging for her "son" Ascanio (fathered by Aeneas) to be "wedded to the wisest nymph ever born of divine blood". This "Silvia" is the daughter of Hercules and, without ever meeting Ascanio, is in love with him thanks to Cupid. But she's not sure whether Ascanio is a vision or a reality. Much confusion ensues.

The remarkable Europa Galante under its inspired violinist/director, Fabio Bondi, added more confusions with the startlingly pretty Sunhae Im singing the stratospheric male-soprano role of Fauno, a shepherd, who appears long before "the wisest nymph", so bagging the love-interest role first. And, naturally, Ascanio is a countertenor....

In such a long evening, only Mozart's ravishing music, pre-echoing things to come, and an exemplary performance allowed this piece to stay its welcome. In the ferociously difficult coloratura, Sunhae Im was outstanding. Patrizia Biccire, Carlos Mena, Anna Chierichetti and Markus Schafer completed the impressively able cast.

Splendid sounds were drawn from Bondi's tight orchestra, the natural horns, trumpets and drums suitably ceremonial. A marvellous MM beginning.