Dance: Yes, there is life after Fonteyn

Ondine Sadler's Wells, London

When the fourth and last of Ashton's full-length works was picked for its current Royal Ballet revival, there was a widespread wrinkling of noses. Ondine, first performed in 1958 and very little since, holds for some a very mothbally smell.

This ballet has never had a good press. On its first outing the plot was deemed thin, the designs old-fashioned, Henze's music obscure and difficult. Most damning of all, it was seen universally as a vehicle for Fonteyn and Fonteyn alone. Without her, it was said, the work didn't exist. Which all goes to show you can't trust the taste of the past.

At Sadler's Wells last week, Ondine was revealed as a masterpiece. They don't make ballets like this any more, and that may be part of its appeal. Lila de Nobili's sets not only conjure up Gothic castles and misty forest glades to ravishing effect, but revel in the kind of low-tech theatrical devices designers daren't try today for fear of looking naive. But unashamed simplicity is their charm.

In the shipboard Act II, a painted sea rises and falls to give a queasily real sense of ocean swell; in the build-up to a storm, fluttering fringed shawls make effective froth and foam. Tricks of light conspire to show the sprite Ondine disporting herself on the waves' surface. Only the Shadow Dance - Ashton's nod to the 1843 ballet version of the story, in which the mermaid duets with her own shape - failed to deliver. Perhaps something was amiss on Thursday: I failed to discern any shadow at all.

But it wasn't hard to see why this ballet was tagged "a concerto for Fonteyn". Despite some atmospheric group dances for naiads and tritons and other slithery things of the sea, and a lively showpiece of a harlequinade, all the dance invention homes in on the central ballerina. And what a challenging role it is: technically, of course, with frond-like, aqueous arms combined with teasing, quicksilver lightness, but principally as a feat of acting and musicianship.

Fonteyn, famously, had it all. But so too does Sarah Wildor, who, with her porcelain blondness and fine profile, is arguably even more alluring. When, during Thursday's shipwreck, her gauzy wisp of a costume accidentally ripped from the breastbone down, not a soul in the house was complaining.

As in Motte-Fouque's tale of 1811, Ashton's source, Ondine is a water nymph without a soul who breaks the laws of nature - fatally - by marrying a mortal. On their first encounter, Wildor's trembling curiosity is touching, her glee on discovering Palemon's heartbeat tenderly comic. Sensuality is only half the story. Wildor conveys such vivid delight in her watery element that you almost see oxygen bubbles popping round her as she dives and frisks, and rides its swirls and eddies.

It helps, of course, to have a stage-lover she can really fancy, and Thursday's audience was treated to a true-life coupling by default. Injury in an earlier cast had prompted the hurried drafting-in of Adam Cooper, Wildor's beau (and now ex-Royal Ballet) and, my goodness, something really sparked between them. How often have we heard that what this company needs is a partnership with true romantic charisma? Well here it is: the real thing. Wildor and Cooper sizzle. And although choreographically the part of Palemon hasn't much to go on - he's what Ashton himself termed one of his "handsome dummies" - Cooper invested its small stock with such hungry, muscular fervour that the role became almost heroic.

As for Henze's score, one can only conclude that taste has undergone a seismic shift since the 1950s. OK, so there isn't anything you can hum (which is what Ashton had been angling for, God forbid). It is grand, moody and vibrantly coloured, its opulent iridescence recalling the sound world of Debussy, its scope so broad and free that the choreography seems swept along on its current, not bounded by its structure. Ashton, in an attempt to placate the composer who at the time suspected his score did not please, told him its climaxes were "better than Tristan". It's certainly among the best sea music I've heard. And under the baton of Andrea Quinn, the Royal Opera band sounded glorious. Clearly, on the strength of this revival, Ondine should be brought back into the regular repertoire, and sharpish.