The black cannon onstage rolls forward and booms, blasting a perfect ring of gray smoke that floats over the heads of the people who have come to see the much-talked-about musical "Martin Guerre." The audience looks up, and the real smoke fills the theater. A few people cough.

Claude-Michel Schonberg, who composed the music for "Les Miserables," "Miss Saigon" and now "Guerre," is sitting seven rows back under the dark cloud of cannon fire and facing the raked stage. From his gold crushed-velvet seat in the Fisher Theatre, he watches and listens. Not to what the people around him are seeing and hearing. For they are gasping at the blast of the cannon, mesmerized by the burning wall onstage, hoping against hope that things will turn out all right for Martin Guerre and Bertrande--that for once a lie will turn out to be the truth and the truth to be a lie. And they are caught up in the music of this very man sitting quietly among them in a black turtleneck.

Schonberg is looking for what the audience doesn't see, can't see because the audience doesn't know the story the way he does. These theatergoers have not lived with the characters inside their heads for more than eight years.

This show is headed for Broadway next spring, and still it is not ready. Ninety-five percent of it, its creators say, is finished. But there is that other 5 percent, like a missing dash of salt. The missing 5 percent is all that drives Schonberg and his collaborators.

"A work of creation is unfinished and never satisfaction. At one moment, you must stop," Schonberg says. "But the very small detail, maybe you will never realize it. For us, it is very important."

He waits until just before intermission to leave his seat and hurry to the back of the darkened theater. There he whispers to his creative team. He is in Detroit to work with the cast, to revise those minute details, to "remind everyone why we wrote it. And to protect the baby." There are notes to change, words to capture before "Martin Guerre" moves on to Washington in late December. (The show opens tonight at the Kennedy Center Opera House.)

The 5 percent hangs there. Something. A note, a word here, an emotion there. So small, so minor that only the creators would know.

"I'm not in the theater to enjoy the show," Schonberg says later. "The music or lyrics I don't love." He knows the music, every note, every rhythm, every bar. "It is like a woman with no mystery for me," he says. "I can't love her. This score has no mystery for me."

Filling In the Blanks

"Martin Guerre" is the third collaboration by Schonberg, lyricist Alain Boublil and producer Cameron Mackintosh. The other musicals--which are not just any other musicals--are "Les Miserables" and "Miss Saigon," both bigger than big in London, on Broadway and everywhere else.

"Martin Guerre" is an old story--a French legend, really. Its title character marries too young and goes off to war, leaving his young bride behind without consummating the marriage. But when he finally returns seven years later, he finds his identity has been stolen. A man who looks like him has stolen not only his name and his life but his prized virgin bride. This is all happening in the 16th century, when "two look-alikes were as strange as two suns that sometimes appeared in the sky," someone once wrote of the tale.

The wife is torn between the two men: her husband, who she says never loved her, and the man who later claimed to be her husband, whom she loves. Here is where a lie is better than the truth.

This legend has been told and retold since 1560 and has inspired two films: Daniel Vigne's "The Return of Martin Guerre" in 1982 and its 1993 remake, "Sommersby," starring Jodie Foster and Richard Gere. The musical "Martin Guerre" was expected to be huge, completing a trilogy of powerful musicals by the team.

But "Martin Guerre" has struggled publicly. When the show opened in London in 1996, the reviews were mixed, Schonberg recalls, conceding that the show wasn't working. So he and Boublil went back to the beginning--writing and rewriting.

"We needed to finish it," Boublil said. And with a living show, they had the power to do just that. "Painters cannot go and say, 'I have not finished my painting.' They cannot add a touch of blue or red, because the painting is now in somebody's house. But we can. We can work and write and rewrite until we are happy."

Boublil and Schonberg et al.'s "baby" has had to grow up in public. The London critics pricked it with diaper pins: It was too big, it weighed too much, and the audience could not understand what it was saying.

"A lot of things were wrong," Schonberg says. But, he continues, there were reasons for that: The two earlier shows, after all, had Victor Hugo and "Madame Butterfly" as source material. "Guerre" was only a tale that had been told and retold, and Schonberg and Boublil had to fill in all the blanks.

Growing Pains

Schonberg is sipping his coffee in a Java Shop down the street from the theater. He takes a fork and breaks a piece of cheesecake. He is recalling the long evolution of "Martin Guerre." Of the 1996 original, he says, "This show was not the show we wanted to write. Too many people were too soon on board trying to help, putting in ingredients from 'Les Miz' and 'Miss Saigon.' But once you start working on a show, it's like a 747 taking off."

It can't be stopped.

And the critics were right, Schonberg concedes. Some of them, at least.

Not, however, the ones who said the show was too complicated. "That is stupid," Schonberg says. And certainly not the critic who said that there was not even one song in the score that you might hum as you walked up the aisle after the show--an old complaint in the musical theater. That one irritates him most.

"That has nothing to do with heart and creation," he says, exasperated. "That is not the purpose of a musical. The purpose is telling a story. I don't give a [expletive] about writing a hit song."

But back to the critics who said three years ago that the show was confused: "They are bloody true."

He adds, "Critics have a right to like or not like a show. They don't have the right to give you an interpretation of what is going on in your mind."

For the creative team, "Martin Guerre" has been a saga. "It has been a long struggle," Boublil says from his flat in Paris. "Seven or eight years of writing and rewriting. It is a difficult story to try to put onstage. It has gone from a medium-sized version to the show in London, which was big. Now we are back to the version which is exactly what we wanted to see onstage. 'Martin Guerre' opened in America."

After its critical roasting, the initial London engagement of "Martin Guerre" failed to catch on in a big way with the public. But Mackintosh, whose producing credits also include "Cats" and "Phantom of the Opera," doesn't give up easily. He, Schonberg and Boublil simplified the story, and the songwriters rewrote some of the songs. Mackintosh then closed the original version and reopened the show. This time, the critics were happier. The reborn "Guerre" has some entirely new songs, including one called "Live With Somebody You Love," which Boublil said he wrote after reflecting on his own marriage of 20 years.

The new "Martin Guerre" won the 1997 Olivier Award for Best Musical. It has grown up a lot. And now it has come to the United States, where in both Minneapolis and Detroit it has received flattering reviews.

But the question remains: Has it grown enough?

Relentless Drive

Schonberg leaves the noisy cafe and waves thank you to the coffee tender. He is walking back to the theater. He has a 1 o'clock meeting with the show's other creators, and he doesn't want to be late.

A wet snow is falling in Detroit. Everything is gray. Schonberg is wearing an olive cashmere coat with a black scarf. The olive coat seems to be the only live color on the gray street. He steps into the street. A car is coming, and you wonder, will he stop and let the car pass? Who will relent? The car, with its two tons of steel, or the composer with the great force of new music playing in his head and the intensity of one who has the last piece of a musical to finish?

Schonberg keeps walking, not changing his pace. It is the car that slows. You wonder whether he even saw that car. And you think it must be the music blasting in his head.

The Music Chose Him

Schonberg's parents were Hungarian Jews who had moved to a village west of Paris. His father was a piano tuner, and his mother stayed home to raise Claude-Michel and his older brother and sister. Claude-Michel knew early that his home town was too small for him. "Like all ambitious people, I liked big cities."

Even as a child, Claude-Michel had a sense of himself, a superior ear. By the age of 7, he knew two or three operas by heart. And he was able to produce on the piano anything he wanted. He told his piano teacher one day that he didn't want to play other people's music: "I want to play my own."

The teacher told him that was nice, "but first you must learn what other people have done."

There was no single moment when he decided he would be a composer, he says: It was the music that chose him. He remembers the childhood rapture of listening to music so beautiful it paralyzed him. "My mother took me to my first department store," where the music was pumped through speakers. As they climbed the stairs, Schonberg was struck. And he stopped. He heard a melody. "It was like reaching paradise. I was paralyzed. My mother said, 'What are you doing? You will get lost.' " But the little boy could not move. "There was magic in the music."

It was the shimmering Prelude to "Lohengrin," one of opera's most famous pieces.

'Like a Life Jacket'

Back in the Fisher Theatre, Schonberg is again sitting on a gold crushed-velvet chair. He has flown here from New York, where he worked with the cast of "Miss Saigon." He was scheduled to fly the next day on the Concorde back to Paris, where he lives with his wife, Beatrice, who is a television anchor, and their two children, but the flight has just been canceled because of a "bloody" strike. He is alone in the theater, and a stage manager is checking out possible flights out of Detroit this afternoon. He needs to get back.

But now someone has come to ask him questions about who he is and how he does what he does.

And he answers what is asked. He has answered these questions before, and he is in a hurry. He is ever aware of the time.

So let's mix it up: Won't he just play the piano?

You know, give a demonstration. Maybe show how he creates music?

There just happens to be a piano in the theater lounge, and it is sitting there waiting for someone like him to touch its keys, make it play something it has never played before.

This must be the most annoying question of all.

"I am not playing the piano," he says. "I am not a pianist. I am not an entertainer. I play only for work."

For the piano is his best enemy. He fights with it. For seven to eight hours each day, they toil--he and his piano. The piano gives him pain. And, sometimes, it gives him pleasure. The pleasure is fleeting, he says--15 seconds at most. But in the 15 seconds when he knows something is good, some original music is born. Then, just as quickly as it arrived, the pleasure is gone.

But he would give the world for those 15 seconds.

Oh, what glory when the music comes, wherever it comes from.

Where does the music come from?

"It is very, very difficult. Even the closest people around me don't know. I don't know how I do it, and I don't want to know. I want it to be still a mystery for me. Is it inspiration or is it someone dictating to me? Is it coming from God? Is it coming from the Devil? I don't know."

Perhaps, he suggests, there is a defect in his personality that brings the music, and if there is, he doesn't want anybody to fix it. "I don't want to be balanced. What is interesting in a person is the defects," he says. "The most boring person on Earth is a saint."

When he is creating, "I sit down at my piano. I close my eyes. I see what is happening onstage. The music is coming right or wrong." To finish three or four minutes' worth can take a month, he says.

It used to be that it took Schonberg a week to know whether what he was writing was "crap." But "now it takes me a few seconds to realize whether it is right or wrong."

To hear him tell it, there are clear reasons when that happens:

"When I'm a bad composer, it's usually because the script is wrong. When we have a problem with the score, generally it's because the book is wrong."

But always, good or bad, he is writing as if his life depends on it.

"You must write like it is the last moment of your life. It is like a life jacket. If you are not writing, you are dead."

Final Notes

Schonberg is in the theater's lounge going over more changes, changes so minute you wouldn't notice them.

"I think structurally it is working," says one of the producers. "But we need to digest it, distill it to its essence and get it right."

"We are suffering from innocuous emotion," says an associate director.

"Do we get into the singing too soon?" asks the producer.

Schonberg is nodding. "This will add something to the passage of time. It will be a painful sense of superstition, and it is part of the behavior you don't have anymore today--primal human behavior when he is chasing Bertrande."

They are working on a transition. The audience must have time to think and know the transition is coming so there will be no applause before the scene is finished.

"Instead of saying paadada, say padadeedee." Schonberg sinks in his chair. He's trying to solve the problem musically.

A producer offers: "In English, it is not doing what you want the lyrics to do." He keeps pounding. "There is nothing about the music that is off. I think it is the lyrics."

Schonberg twists the short hair behind his ear. He is not convinced.

The producer continues. And we hear snippets of creation.

Finally, Schonberg leaps from his chair. "The note has to hit like that," he says firmly, stomping his foot for emphasis.

The piano is in the middle of the creative team. The composer leans over. He flips the pages of the music book. He sings what he thinks should be changed.

But he doesn't touch his best enemy, the piano.