It would be tempting, but erroneous, to suggest that ''The Lighthouse'' got its start in life off Flannan Isle in the Outer Hebrides in December 1900. That's when three lighthouse keepers disappeared without a trace, leaving behind them only mysterious half-clues and the stuff of local legends. And, to be sure, the mystery was born about that time.
But the Peter Maxwell Davies opera came to life during three intense weeks on an island wrapped in ''wind and the sound of the sea - sometimes violent, sometimes so quiet you can almost hear the frost grow,'' as Davies describes it in his Boston hotel room. His work is now having its American premiere at the Boston Shakespeare Company.
Davies had heard the story of the three lighthouse keepers many times. He says the opera grew from an idle curiosity to a working model as he thought more and more about ''the fascinating technical challenge'' of making it work as musical theater. He wrote out the text himself in two weeks, in his Orkney Island retreat, all the time turning over the weights, gestures, and structure of the music in his mind. Then he dashed off the score in a week.
You have to keep telling yourself this, as you listen to the densely woven textures of the work, the tightness and ferocity of skill with which it is hammered together. Written in one week? Stage director Peter Sellars and conductor David Hoose had been toiling over the piece for months.
A week before opening, they were hard at it in the darkened theater of the Boston Shakespeare Company. Sellars was sitting in the gloom of the auditorium, his face a smudge of light, as Hoose took the orchestra from one technical challenge to another. And T. S. Eliot's line - ''These fragments I have shored against my ruins'' - would have made a perfect subtitle to the process. The music, so pristine in its austerity, came by in broken flashes, like sea glass catching the winter sunlight.
In a rehearsal break, Hoose sat quietly reflecting on the in extremis quality of the music at its most intense moments; also ''the incredible brutality - and beauty - of the piece.''
''We wanted to treat it as a piece of music - not opera,'' he said, ''finding the essence of the piece through the music, rather than manufacturing . . . staging and dramatic situations.'' Sellars and Hoose have plunged into the music discovering the dramatic situation in ''the pitching, the phrasing, the way the music breathes.''
In a way, all of this is, or should be, standard procedure for staging an opera. But in Davies's work, the task becomes more imperative, because he writes his own libretto out of the musical impulse. And it makes every bit of sense to have the orchestra members on stage and the spare line of the action working around and above them, ''because they are the ocean on which the singers are tossed,'' as Sellars said and the action is only a prism to see the music through.
What you see is a work that revolves around a sort of ''Bermuda Triangle North'' mystery, one that is almost completely devoid of warmth and the soft pulse of life. ''The Lighthouse,'' however, makes a virtue of its austerity and the bloodless approach to its ends.
All of this makes it a supremely demanding work for audience and performers. But the demands are worthwhile, because ''The Lighthouse'' gives you this bracing, sometimes terrifying vision of the cold sea and its hidden mysteries.
Isolating himself on that Orkney island, without a telephone, and with nothing to think about or do except write music, Davies took on some of the coloration of his habitat. The craggy, moody air one associates with those north Scottish isles is very much about him, even in a Boston hotel room. He has dark hair, blue eyes, and a pale countenance. He does not suffer fools easily. There is a mixture of forbidding silence and sudden humor.
All of these qualities are evident in ''The Lighthouse.'' These, and a fantastic musical mind, one that can take a local legend and turn it into a chilling musical fortress. Peter Maxwell Davies's opera doesn't exactly take us to the Outer Hebrides during December 1900. But where he does take us is, in its way, more mysterious and chilling.