Skellig came out of the blue," recalls David Almond, "as if it had been waiting to be written." The award-winning author and former teacher was 47 when his breakthrough book, the tale of young Michael and the mysterious winged creature he discovers in the ramshackle garage of the new family home, was published in 1998. Selected last year by the Carnegie Medal judges as one of the 10 most important children's novels of the past 70 years, and translated into 35 languages, Skellig has taken flight in ways Almond never imagined. As well as being adapted as a radio play, it's been staged, notably by Trevor Nunn in a huge hit for London's Young Vic in 2003, while a film - starring Tim Roth as the baffling part-owl, part-angel Skellig - will be released next year.

So it came as no surprise to Almond when the American composer Tod Machover and British theatre director Braham Murray approached him with the idea of turning it into an opera.

"When I was writing it, I felt involved in a soundscape around the words - the dawn chorus, the hooting owls, the creaking of the derelict garage, even the slurping of Skellig," he says. "And when I had finished the story, I found myself referring to it in musical terms, likening it in rhythm and pace, and perhaps even occasionally mood, to Purcell or Monteverdi."

However, Machover - described by the Los Angeles Times as "America's most wired composer" - could scarcely be more different from those baroque masters in his use of new technology. Known for his synthesis of acoustic and electronic music, for marrying symphony orchestras with interactive computers and mixing operatic arias with rock songs, the professor at the Massachusetts Institute of Technology's Medialab (where he runs the Opera of the Future Lab) has a reputation for breaking traditional artistic and cultural boundaries. In 2002, he brought some of his newly-created range of music toys - his "beat bugs" - to Glasgow, enabling children with no musical experience to join Joshua Bell on the spooky- sounding "hyper-violin" and the BBC Scottish Symphony Orchestra in Machover's Toy Symphony.

Machover was immediately attracted to the the eerie and enthralling Skellig novel, especially its lyrical streak and the strong, simple dialogue, with which Almond describes and defines the characters, and which the author has retained in the opera libretto he has fashioned.

"The contrasts in the story are shaped by sound throughout," says Machover. "Skellig's world is described by smell, it's true, but the colour and transformation of the characters are achieved through a myriad of unusual sounds - from scuttling insects, twittering birds, the crying of a baby and the noise of traffic to laboured breathing and beating hearts - all of which suggested to me the melodies and musical textures that could bring the novel to life in a new form."

The composer also likes stories "about having hope restored and about hope engaging with the world". That power of belief is what made Skellig stand out for director Braham Murray, the mystical link between a sick baby fighting for her life and the curmudgeonly Skellig, to whom the baby's brother gives sustenance - the remains of Chinese take-aways, aspirin for his "arthur-it-is" and Newcastle Brown ale - as well as, through kindness, the will to proceed on his journey.

Rooted in the north-east, and the first opera to be commissioned and created by The Sage, Gateshead, Skellig, says Almond, "feels like a homecoming".

There is a connection between Almond's own childhood and the fictional Michael, whose relationship with Skellig develops against the background of his baby sister's heart condition. Almond himself had a sister who died as a baby when he was seven. Yet, even for the author himself, Skellig - a creature with curious humps instead of shoulder blades and a taste for spiders, dead mice and decayed bluebottles - resists easy definition. But while addressing a young audience, the opera (like the book and the play) taps into a depth and a profundity which Machover believes will connect with adults just as powerfully.

Geordie accents are not obligatory for the seven soloists, says Machover, which must be something of a relief for the singers. Tackling a new opera is hard enough without trying to sound like Ant and Dec at the same time. The part of the crackly, croaky Skellig - involving unusual vocal techniques - will be taken by the versatile singer-actor Omar Ebrahim, while Michael's father is sung by Kilmarnock-born Paul Keohone, who recently proved his affinity with new music in Scottish Opera's innovative Five:15 project.

The tenor part of the boy Michael was, according to Skellig music director Garry Walker, "the biggest problem in a difficult casting process that was especially tricky because of the need to balance youthful looks with the maturity and experience to cope with the vocal and dramatic demands on the singers". Newcomer Matthew Long takes on the challenge of Michael, a role that requires "singing almost as if speaking". The boy's mother, given longer, spun-out lines including a lullaby, is sung by Sophie Daneman, who has carved a reputation for her interpretation of early music, taking us back to Almond's instinctive comparison of the novel Skellig with the indefinable purity and expression of feeling of baroque music.

The soloists, says Machover, are tagged with individual turns of phrase, "motifs, melodies, specific intervals", adding quickly: "But not as in Wagner." Each character is musically distinct from any other in rhythm, range and complexity and, according to Walker, "the score is leaner than many of Machover's works, treading a fine line between being cutting-edge and highly approachable, with particularly accessible and beautiful choral writing".

And it is the chorus, made up of young people auditioned from around the north-east and trained in vocalising and movement, which plays a pivotal role. "These teenagers are the bridge between the non-musical and the musical sounds," explains Machover. "They imitate or respond to a kind of audio-score, their parts reinforced by an electronic tapestry which is sometimes heard by the audience and sometimes picked up only by the chorus.

"It's a new idea which I hope will help to express the kind of intangible experiences and thoughts of the protagonists, taking the performers and, more importantly, the audience, to a place in between the words and beyond the action." On stage for almost the entire evening, the chorus has been choreographed by Mark Bruce. Almond has been surprised by how effective a metaphorical replacement the movement has become for the story's specific sites and scenes.

Machover promises some sleight-of-hand when it comes to musical effects, particularly in the relationship between the instruments of the keyboard-augmented chamber orchestra and the ambient soundscape which evolves in each performance.

There's a layer of music which will envelop the audience, thanks to new software which allows noises to creep in and up on the audience, surrounding the listener with a floating halo of delicate 3-D sounds. It seems likely that, in its new operatic guise, Almond's story will continue to work its extraordinary magic.

Skellig is at The Sage, Gateshead, from November 23-29.