Decadent, debauched and divinely depraved, David Alden’s production of Francesco Cavalli’s 1651 masterpiece is everything one had expected, and then some. The Royal Opera has been tardy in staging anything by this high-spirited master of high-camp Baroque — Cavalli, I mean, not Alden (though he’s new to Covent Garden too). But this show, which started life with much the same exuberant cast in Munich three years ago, is worth the wait.

Visually, it’s a riot of 1960s kitsch. The loudest thing in the whole opera is Paul Steinberg’s Vegas-style hotel set: a gaudy clash of compellingly hideous stripes, inside which the goddess Diana’s troupe of leggy lovelies drift around in groovy leopard-skins, and Pan’s grotesque gang of bestials (fabulous costumes by Buki Shiff) do bad-boy things to a hapless shepherd. And sexually, there’s certainly something for everyone, even those who prefer the animal kingdom. What with Sapphic gropes, masturbation, transvestite rape, and a randy goat with a waggling willy (only plastic, vicar), this isn’t an evening likely to receive a glowing endorsement from the Republican vice-presidential candidate.

But what’s it got to do with the original La Calisto? Well, Alden cleverly manages to be both saucy and serious. He has a ball with the sex-comedy shenanigans, as randy gods have their wicked way with trusting mortals. But particularly at the heartbreaking conclusion — as the duped and dumped nymph Calisto is given a glimpse of heaven, only to be turned into a bear — he brings out the legend’s pathos. Indeed, he boldly restores the serious bits of Ovid, notably Calisto’s pregnancy, that Cavalli cut.

It’s fitting, then, that the most poignant singing comes from the mistreated humans — Sally Matthews, who produces ravishing tone and looks gorgeous as Calisto (her own pregnant curves add a touch of extra verisimilitude), and the counter-tenor Lawrence Zazzo, who has the most touching arias as Endimione, the noble shepherd besotted with Monica Bacelli’s hilariously hypocritical “chaste” Diana.

Around them are riveting performances — Dominique Visse’s repulsive half-goat Satirino; Umberto Chiummo’s wickedly suave and lecherous Giove; Markus Werba as his pervy procurer Mercurio; Veronique Gens as his exasperated wife Giunone; and Guy de Mey, who surely wins the Mincer of the Year prize in the pantomime-dame role of Linfea.

Ivor Bolton and a composite orchestra of period-instrument specialists supply lush, alert accompaniments, superbly tailored to the drama’s mercurial twists. Musically, Cavalli may not reach the sublime lyrical heights of his mentor Monteverdi. But these singers pace and ornament the ebullient tunes with such flair that there’s never a dull moment.

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