OPERA: The Juniper Tree Almeida Theatre, London

If family trees were real trees, most would be suffering from nasty withering diseases. In Roderick Watkins's The Juniper Tree, the titular tree is where dead relations are buried, but this particular family's tree is also the site of rebirth, albeit bought at a terrible, if familiar, price: the wicked stepmother must die.

Patricia Debney's libretto, balancing whimsy with distress and heartbreak, derives from one of the Grimms' bleakest stories. Father, a worthy artisan, loses his wife after their son's birth. He buries her under the juniper tree, and marries again. The stepmother already has a daughter, hates the son, and eventually kills him. She makes dinner of the boy, and serves him to the father. The distraught daughter buries the child's bones under the same tree and, from the mingled remains of mother and child, a bird is born. Happiness returns, but only after a gigantic millwheel crushes the stepmother.

Although this is Watkins's first opera, he understands the basics: first, let your words be heard. Second, give your orchestra a distinctive identity. That is this work's greatest strength. It's apparent from the wonderfully sinister and suggestive first moment, when a minatory bass clarinet on one side of the stage is answered by a shimmering harp on the other. By dividing his orchestra (the London Sinfonietta under Markus Stenz), Watkins builds a musical arch in which certain groupings develop close relationships: on one side, clarinet, flute and oboe; on the other, harp, horn and bassoon.

There is a brief electronic interlude, quite effective even if its timbres closely echo the on-stage instruments. Watkins is less successful with the voices, which are given mostly syllabic phrases until the emotional temperature rises, when piercing melismas fly in all directions. There's a dramatic logic in that, but the effect of restricting vocal ornament to moments of high drama is to remove weight from the intervening passages, so that, were it not for the ear-catching orchestra, attention might wander.

David McVicar directs, and provides the predictably lumpen costumes, but he hasn't found a consistently involving physical language for his cast, while Michael Vale's revolving set gives us the family home of pre-industrial Hovis ads, a frame for the action rather than part of it. Still, there are heart-stopping moments, notably when the bird-boy wraps a comforting wing around his father; but too much time is spent on the wringing of hands and clasping of temples.

The cast is nevertheless a good one, with Penelope Walmsley-Clark outstanding as the Stepmother, and Alison Kettlewell radiant as the Mother. Robert Poulton's Father sounds terminally melancholic, but his stage presence is rather wooden, while Louise Mott struts and frets neurotically as the daughter. Timothy Webb's Boy is touching, particularly in the scenes with Kettlewell, and it's easy to hear why The Juniper Tree was so successful when premiered at this year's Munich Biennale. Still, I left feeling that, for Watkins, as for so many contemporary composers, the unanswered question remains: "What are we to do with the voice?"

Further performances: tonight and tomorrow, 8pm. Booking: 0171-359 4404