Royal spiral into horror

Dance-goers have a curious habit of referring to three-act ballets as "full-length", as though any other kind is somehow incomplete. It is like a concert-goer suggesting that a Mozart string quartet is very pleasant, but one day it will grow up to become a "full-length" symphony.

Seeing Sir Kenneth MacMillan's Mayerling after a decade, though, one is tempted to agree: compared with the glories that he has poured into this endlessly rich, endlessly rewarding work, other ballets can seem incomplete, and not "full-length" at all.

Mayerling tells the story of Crown Prince Rudolf, the son of Emperor Franz Joseph and Empress Elisabeth of Austria-Hungary. As the ballet opens, he has just been married off to a Belgian princess, whom he despises. His ex-mistress, Larisch, retains her power over him by bringing him new girls, and now she produces Mary Vetsera. It is a fatal meeting. Rudolf, a lonely and despairing mess, is goaded on by Vetsera, a hysterical proto-groupie, and together they descend into psychosis and, ultimately joint suicide.

That is the plot at its very simplest. But complexity in the hands of a master like MacMillan never means confusion, only a deepening of our understanding of these damaged psyches.

Under the new and happy regime of Monica Mason, everyone performs with total commitment. Genesia Rosato, as the Empress, is as vain and frivolous as Elisabeth was in real life - she is every inch the woman who recorded her weight in her diary before she bothered to note that that morning her son had killed himself. Mara Galeazzi has a wonderful time as the sharp, predatory Larisch, and yet lets us see that this is a woman who is fighting for survival.

Alina Cojocaru plays Vetsera, remarkably, as a delicate, tremulous wanton. Cojocaru has been a principal for only a year, but every performance gives more evidence that she is a once-in-a-lifetime talent.

But the honours of the evening go to Johan Kobborg. As Rudolf he is barely off-stage. He begins as an unhappy, repressed man; gradually he spirals down into drug-addiction and violence, until death becomes the only possible freedom. Kobborg's every gesture conveys the horror of Rudolf 's life. His dancing is as immaculate as ever, and his acting is now on an altogether new plane.

This is MacMillan's masterpiece, and the Royal Ballet has done him proud. Let's hope Mayerling will now take its rightful place in the permanent repertory.

Until 16 November. Box office: 020 7304 4000.

Mayerling:The Royal Ballet