Lucky dip into the myth kitty

The debate about the relevance of opera today, especially fairy- tale opera, has recently been revived: in the same way as critics call for the Great Novel of Britain in Decline, so musicians and music critics have exhorted composers - or perhaps, strictly speaking, librettists - to confront contemporary issues. Nixon in China, not Orlando; The Plumber's Gift, not The Mask of Orpheus.

The composer John Woolrich, when he asked me last year to write a libretto for him, specified that he wanted a fairy-tale: he sees the tradition of opera performance as conjoined with the carnival art of serio ludere (playing seriously), with puppet plays and street games, with conjuring and tumbling, stretching back to travelling players and the commedia dell'arte troupes who were visiting England from Italy in the 16th and 17th centuries. Their art didn't feed foolish and dangerous fantasies, like the romances Cervantes mocked when he inaugurated the modern novel. The comic repertoire of bawdy and magic dramatised man-eating ogres, seven-league boots, caps of invisibility and talking animals in the same breath as it boldly attacked prevailing marriage arrangements, overweening aristocrats and scheming lawyers. Woolrich also stipulated he wanted the theatrical frame to show: the opera should revel in its own artifice and manoeuvres, making a virtue of a restricted budget, so that role-doubling and costume-changes became part of the spectacle.

The result, In the House of Crossed Desires, takes stock characters from the commedia tradition, like the wicked old miser and the likely lad on the make, and sets them within a fairy-tale plot that's a freely shaken mixture of several famous stories: aficionados will notice bits of Donkeyskin and Tattercoats, of Rumpelstiltskin and The Sandman, of the Grimms' Mother Holle, Angela Carter's The Magic Toyshop and, above all, of The Golden Ass. Apuleius's metaphysical romance gives the opera its central motif: the young man who's turned into a donkey.

Shakespeare knew The Golden Ass well: "Bless thee, Bottom, bless thee! Thou art translated," says Quince when he sees sweet bully Bottom the Weaver with his ass head on. Metamorphoses of this sort are sure indications that we've entered the territory of the wonder tale; and the principal aim of magic is transformation. If the formula "Abracadabra!" failed to bring about a change, to turn lead into gold, or at least pull a rabbit from a hat, it would be worthless. The current show at the Wellcome Institute of the History of Medicine entitled Abracadabra surveys the interwovenness of magic and medicine, of supernatural quests and scientific inquiry; implied by the connection is the capacity to bring about a transformation: in the sphere of medicine, a cure; in the sphere of magic, reprieve, requirement, revenge (and cure, of course, as well). Spells consist of formulae that bend reality to their shape; they're commonly verbal, though they may be meaningless, and they're often musical. The Wellcome Collection has some remarkable manuscript examples of popular grimoires or spellbooks like The Key of Solomon. One gives a "very effective remedy against impotence": the sufferer must write down certain words and ciphers before daybreak on a golden tablet or, failing that, a horseshoe, found by chance in the street on a day under the influence of Saturn; then it must be plunged deep into the banks of a stream and, in nine days, the trouble will be over. "The little needle will be untied altogether, and the one who tied it will begin to suffer from another problem."

In the House of Crossed Desires features a number of disturbing magical transformations wrought by spells and songs: the wizard flies away as a bird, the heroine is transfigured into a rose-garlanded doll, and the Goddess Hope descends at the end and makes a few dispositions of her own. Such trifling with the laws of physics is exhilarating in itself: a stage direction that reads "Luca turns into an ass" has its blithe side, in the writing as well as the staging (it seems). But there are also serious undernotes to the playful reasons for choosing wonders and improbabilities, for refusing the replication of ordinary laws and the naturalistic representation of modern life.

Fairy-tales can smuggle a disturbing theme across the borders of consciousness without pushing the receivers' faces in it. They've been told to children and youths for centuries for this reason: they're stories about family strife and sexual danger, about intellectual curiosity and impatience with social hierarchy, but they remain in disguise, in the land of far away and long ago and once upon a time. The disguise means that certain themes can be tackled which, stripped, might be censored out: that donkey business in The Dream covers a multitude of sins without ducking the issue of sex.

But censorship, as everyone knows, has frequently struck the fairy-tale just the same. Rapunzel, in the Grimm brothers' earliest version, describes how the heroine pulls up the prince by her hair into the tower and enjoys his company for a while until, one day, she asks the Old Witch, "How is it that my clothes are getting so tight?" So the old woman realises that her ward has been up to no good, and cuts her hair and smashes the tower and blinds the prince and other such openly coded acts. But the Grimms became uneasy about the explicit character of Rapunzel's plight, and they changed her question to "Why are you, Old Mother, so much heavier than the prince I pull up by my hair when you're not looking?" Thus making a complete ninny of Rapunzel and a nonsense of the fairy-tale, draining it of its traditional warning against the appeal of passing wolves.

Fairy-tales are open to transformation, and the Grimms were working in the fine storytelling mode of adapting material to suit their chosen hearers and readers: in their case, ideals of middle-class urban family decorum prevailed. It is anti-historical to argue that authentic, original versions should be retained. The trick is rather to re-tell them in fresh ways in order to ignite the special pleasure of unconscious recognition for the audience in question - as Carol Ann Duffy triumphantly achieves with her verse version of Grimms' Tales staged last year at the Young Vic to the delighted thrills and squeals of laughter of school parties.

In the House of Crossed Desires attempts to transform some of the recurring motifs of fairy-tale: the vicious old woman jailer, with her threats and her whip, takes centre stage in the part of Greasy Joan, but she is translated, too - if the desired alchemy of music, performance and words works - to become a person with her own past of lost loves, loneliness, and desperate choices. It would have been possible to write the part of this "disreputable hag" as one of the many beaten-up homeless women who sit on the pavements of Kentish Town and the Strand, but the strength of the conventions rooted in both opera and fairy-tale means that she could be established as a person with tremendous economy of means; and, as Helena says in A Midsummer Night's Dream, that most enchanted of all the fairy plays, "Things base and vile, holding no quantity / Love can transpose to form and dignity."

Philip Larkin's gift for the acerbic epigram has memorably stigmatised "dipping into the myth kitty"; but its contents aren't so easily put in a box and shut up and the key thrown away, as his metaphor suggests; they're parts of thought, invisible, stealthy, potent. They form a language of the imagination, and, especially in a medium like opera, they make new moves possible. A composer recasts existing notes and transforms time signatures and plays with given rhythms, so a librettist can attempt to translate the old spells and figures that have proved effective in the past: the star-crossed lovers, the cross-dressed heroine, the cross patriarch, and the crossings of destinies in any life.

n Music Theatre Wales premieres 'In the House of Crossed Desires' at the Everyman Theatre 6 and 10 July as part of the Cheltenham International Festival of Music (booking: 01242 227979). 'Abracadabra' is at the Wellcome Institute, London NW1 to 26 October (0171-611 8888)