"It isn't Goethe that creates Faust, but Faust that creates Goethe," Jung once wrote. His dictum hovers unspoken over Monster, Sally Beamish's first full-length opera, which explores the circumstances that led Mary Shelley to write Frankenstein. The thrust of the work is that Frankenstein's monster was the creation of a woman who both saw herself as monstrous and was deemed so by society, while writing the book enabled Mary to reconcile herself to the trauma of her own existence.

The libretto, by novelist Janice Galloway, encapsulates Mary's remorseless self-laceration in a sequence of interlocking visions that reflect the dreadful events of her life: the death in childbirth of her mother, Mary Wollstonecraft; her father William Godwin's rejection of her when she eloped with Shelley, a married man; the death of her own baby while Shelley was away with his wife. The text is strewn with shards of Romantic poetry, while phrases from the novel gradually force their way into the dialogue.

Beamish underpins the resulting tapestry with a score thick with postmodern allusion. Quotes from Beethoven and Scriabin accompany Godwin's reading of Aeschylus's Prometheus Bound, pointing the way towards the novel's creation and its subtext. Shelley arouses Mary's desire by reading Queen Mab to souped-up Wagnerian palpitations. The orchestral howling that accompanies the father's rejection becomes the demented wail of Frankenstein's creature as the book takes shape in Mary's mind.

The work fails, however, on two counts. Galloway fudges its main thesis - that fiction is the product of real trauma filtered through the imagination - by introducing a character of her own, a French scientist unsubtly called Victor Frankpierre, who provides Mary with both the book's scientific background and her hero's name. The other main problem is that Beamish's angular vocal writing renders much of the text inaudible. Given that the work is about literature, this is particularly messy.

Michael McCarthy's production, too, could be sharper. He employs an all-purpose surrealism, with the characters fumbling around on a unit set, part Piranesi, part Salvador Dali. Some of it is beautiful, but the narrative is woefully unclear, while Frankenstein's briefly glimpsed monster looks like a gay porn icon. The premiere was glowingly conducted by Diego Masson, however, and superlatively played by the Scottish Opera Orchestra. There are also some tremendous performances, notably Gail Pearson's anguished Mary and Stephen Rooke's dreamily lyrical Shelley.

In rep until May 1. Box office: 0141-332 3321. Also touring to Edinburgh and Brighton.