HEARD about the poor deluded ballet-lovers who are demanding refunds from Sadler's Wells? They paid to see Swan Lake, and Matthew Bourne's Swan Lake, they claim huffily, is not. Apparently oblivious to images of feathered chaps seen everywhere in recent weeks, they'd really believed that a group calling itself Adventures in Motion Pictures would stage a fairy tale in which a prince in tights falls in love with a swan-ballerina en pointe.

So let's set the record straight. In AMP's Swan Lake all the swans are men. And the Prince does not go for the girl. Only the crassest spectator, however, would call it "the gay Swan Lake". Matthew Bourne's production is dark, searching and provocative. As in all the greatest theatre, you leave shaken and also stirred.

In the original, Prince Siegfried is unhappy; he disappoints his mother; he becomes obsessed with a woman, magicked into the form of a swan. We suspend our disbelief as we do in fairy stories, as we know we must to have classical ballet at all. Bourne, in his modern-dance version, probes the inner meaning of the fairy tale and with the psychoanalytical insights of our time puts Siegfried on the couch. No suspension of disbelief is required; the swans are all in his mind.

In an inspired stroke, Bourne makes use of the customarily stage-dead time of Tchaikovsky's eventful overture to lay down his themes. Designer Lez Brotherston places a king-sized bed upstage, and on it a prince-sized boy. He is having a nightmare. By the time it has sub- sided we have been introduced to his mother (Fiona Chadwick, a model of Audrey Hepburnesque chic, and cold as a fish) and have noted that she does not take him in her arms. The boy, becalmed, cuddles a stuffed toy swan.

The first scene follows with all the wit and sparkle that Bourne claimed as trademark with his Nutcracker three years ago. A clockwork corgi taken walkies by a palace flunkey is not the least of its quirky delights, and there is no set-piece that does not further the plot or our perception of its characters. The bed-head is transformed into the palace balcony, from which the Queen and her reluctant son deliver the endless regal wave, and the big Act I waltz takes the form of a swaying, hurrah-ing crowd.

The straight Swan Lake requires only one basic scene-change: from palace grounds to lake and back again. Bourne ambitiously takes us in and out of the Prince's bedroom and downtown to a sleazy Soho club before we get anywhere near the water. The club serves to emphasise the instability of the Prince's mind. A tawdry crowd of freaks, tarts and Kray-twin lookalikes indulge in a wild bop that combines gestures from 30 years of disco-dancing. Drunken Siegfried (Scott Ambler) starts a brawl and is thrown out on to the dark street. It is here, beneath a Swan Vestas hoarding, that the plaintive, brooding oboe heralds his vision of the swans, who arrive in the gloom, necks and wings outstretched, borne on others' shoulders. It is a moment of eerie beauty.

As usual, we must wait until Act II for the full impact of the corps de ballet. Even those prepared for the sight of men in white-feathered Bermudas are not expecting this, a muscular mass of preening, strutting, swooping creatures - aloof and predatory. Here lies the germ of Bourne's choreographic inspiration. The swan-leader, Adam Cooper, stands out a mile for his supple sensuality, his leaps as light as featherbedding, his primal animal presence. When he finally allows the Prince to join him in a proud pas de deux the audience shares Siegfried's own awed amazement.

But if no Von Rothbart, no Odile. Bourne tackles the black-swan problem (of his own making) by reintroducing Adam Cooper as a sexually charged charismatic guest at the Queen's party. Tight leather trousers, black tailcoat and even (crikey) a whippy little riding-crop are all props Cooper needs to turn in a dangerously licentious performance that has every female at the party (and in the theatre) in his thrall. Having danced every one of them off her feet - including the Queen, in a frenzied twirl over tables - he finally turns to Siegfried, by now a mass of Oedipal confusion. Is the stranger really the swan? Does he recognise the Prince? For the first and only time there is homo-erotic electricity, both attraction and repulsion. The denouement, when it comes, is seat-gripping. Suffice to say that it involves pistol-shots, a lunatic asylum and a horrific death by pecking.

This is a show that will be talked about for months. The plot imposes nothing that Tchaikovsky's great score cannot amply contain, and in working through its implications and meticulous attention to psychological nuance, Bourne finds a dramatic potency that goes far beyond what dance is normally capable of. He has created a new form of music drama of near-Wagnerian profundity. See it, even if you never want to feed the swans again.

Sadler's Wells, EC1 (0171 713 6000), to 25 Nov.