Tristan & Yseult, National Theatre, Cottesloe, London

Imagine that an emotionally wrenching Greek tragedy had somehow got rudely entangled with one of those irreverent satyr plays that used to round off and put in a wider perspective those tragic trilogies in Athens.

Imagine that an emotionally wrenching Greek tragedy had somehow got rudely entangled with one of those irreverent satyr plays that used to round off and put in a wider perspective those tragic trilogies in Athens. Or imagine that the romping scherzo section of a symphony had been electronically mixed with the sad, slow movement so that you felt that you were listening to both of them in rapid alternation. This will give you some idea of the strange, mind-bending and heart-twisting atmosphere generated by Tristan & Yseult - a wonderful retelling of the famous, not to say infamous, love story that Kneehigh, the Cornwall-based company, has brought to the Cottesloe. The result is one of the best evenings in theatre you could hope to find.

On a recorded soundtrack, the celebrated Tristan chord keeps crashing like some great wounded wave into the proceedings. But the production - cleverly directed by Emma Rice and lit by Alex Wardle in a way that is adroitly responsive to all the shifts of mood - also boasts a swing band, who sit aloft over the wooden disc of a stage. In doing so, the show wrests the myth back from the near-monopolistic might of Wagner and shows it to us from other competing perspectives. History, they say, is written by the victors. But here it's the defeated who get to tell the story - in which, of course, there is agony and ecstasy for our title pair, and just agony for everyone else who enjoyed the dubious privilege of being in the line of fire.

Here, in a piece which starts near the end of the saga and then performs a long flashback, the main narrator is the plain, suburban, somewhat vengeful woman whom Tristan - on the tragic rebound and suffering from permanently unhealable wounds - married for the mad contingent reason that she too happens to go by the name of Yseult. The production is mediated by a chorus of nerdy men in cagoules who are the Club of the Unloved, and form human scenery.

The production executes a little miracle. It allows the crucial bit-players moments of centrality. One of the most haunting, funny and sad sequences is where the female attendant, Brangian (brilliantly played by the cross-dressed Craig Johnson), recounts what it has felt like to be used as a decoy and to lose her virginity in the darkness to the duped King Mark. It allows the wife (all scorched starchiness in Amanda Lawrence's unnerving performance) her embittered cry that love is the "euphoria of impossibility". And yet it manages to show respect and empathy for the lovers (splendidly embodied by Eva Magyar and Tristan Sturrock).

Because of the surrounding irreverence (the absurd flying round on pulleyed ropes, the ship sail as theatre curtain, etc), the pain of their love communicates itself keenly to us. Terrific, for those who long for theatre which takes the mind and heart into an altered state.

To 7 June (020-7452 3000)