True period performance

Opera: ARIANNA; Royal Opera House, Covent Garden, London

Now past 60, Alexander Goehr seems set on completing other men's unfinished business, if not his own. His 1992 The Death of Moses, written for the Monteverdi Choir - and his first attempt to create a modern Monteverdian orchestra - effectively supplied the missing third act of his spiritual father Arnold Schoenberg's abandoned opera, Moses und Aron. Now, in Arianna - teasingly billed as "lost opera by Claudio Monteverde composed again by Alexander Goehr" - he has added a last finishing touch to the restoration work begun by his real father, the conductor (and Schoenberg pupil) Walter Goehr, with his pioneering performances of Monteverdi's Vespers 40 years ago. But when, with so many old debts still to repay, will Goehr ever come into his own?

Borges tells a story, "Pierre Menard, Author of the Quixote," about an early 20th-century French Symbolist poet who aspires to so complete an identification with the 17th-century Spanish novelist Cervantes that he attempts to write his masterpiece for himself - not to copy it, re-create it or update it, but literally to write it, word for word, as his very own work. Naturally, he fails. But the fact that several extracts from Don Quixote are found among his posthumous papers suggests the ultimate feasibility of his plan; and this in turn suggests to Borges a new method of reading, deliberately using anachronism and false attribution to enrich the writings of the past: so might we read The Story of O as if penned by Mother Teresa (or hear The Ring as if Wagner post-dated Freud?).

Goehr, in trying to "compose again" a lost Monteverdi opera, perhaps had it easier than Borges's hero: the latter had Cervantes's original as an ever-present "control" on his experiment; Goehr had only Ariadne's famous Lament (the sole surviving fragment of the 1608 score) to go by, plus Rinuccini's libretto - and, of course, the model of Monteverdi's other extant work. Then again, Menard's mad adventure is a fiction, Goehr's only too real.

To an extent, all modern performances of Monteverdi are arrangements: bass lines survive, not instrumentations; guess work must fill out the staves. In this respect, where Goehr dares to tread, Orff and Henze have dallied before. But Goehr's 16-piece orchestra - with saxes standing in for sackbuts, guitar for chitarrone - sounds well in Renaissance mode, if occasionally (in Theseus' raunchy disembarkation march, say) overly reminiscent of the Nyman Band, while having spare capacity - particularly in its range of percussion and sampled sounds - to inflict typically 20th- century glosses upon its sketchy period pastiche.

Contemporary echoes abound: Theseus debates deserting the sleeping Ariadne over the fretful strum of a solo guitar, just like another operatic Greek hero caught in crisis on a foreign shore (Goehr first sang Monteverdi in a choir trained by Tippett). The famous Lament is first heard in quotation marks - in a scratchy old Ferrier recording - while Goehr's own setting, delivered by Susan Graham's intensely suicidal Cretan princess as she is hauled up from the watery depths like a prize catch at the end of some fishermen's ropes, spirals off into a modernist mad scene akin to Berio's Recital I, with its mentally decaying, Monteverdi-singing prima donna (another case of vicarious completion? There never was a Recital II).

Yet so convincing is Goehr's seicento style, the vocal writing especially - including a ravishing madrigal for the fishermen - it's often hard to remember that the same hand is responsible both for constructing and deconstructing the material. Modernism, though, retreats ever further into the background as the opera proceeds, until only two sopranino recorders, a violin, tambourin and medieval harp, later joined by alto trombone and soprano sax, emerge on stage to celebrate the union of Bacchus and Ariadne, leaving the rest of the band (under Ivor Bolton's needle-sharp direction) to fall silent in their upstage pit, and gently begging the question: is Rinuccini's obligatory happy ending any more "authentic" than Goehr's writing?

It's here, in the finale, that Francesca Zambello's exemplary staging (colour-coded costumes by Alison Chitty; neon lighting by Alan Burrett) really takes off, as a galaxy of pink-winged putti light the divine couple on their heavenly way. On stage and in the score, it's a true period performance. But it begs another question: Alexander Goehr, Renaissance man or modern master?

n To 4 Oct. Booking: 0171-304 4000