ON the face of it, Hollywood projects don't get much simpler than "The Da Vinci Code," a movie being shot in Europe this summer, based on the international publishing phenomenon by Dan Brown.
All the ingredients are there: a blockbuster book with 36 million copies in print, an Academy Award-winning team in the writer Akiva Goldsman and the director Ron Howard (for "A Beautiful Mind"), and an Oscar perennial, Tom Hanks, in the lead, as the Harvard professor Robert Langdon. Sony Pictures, the studio behind the film, would seem well on its way to that rarest of successes: an adult-oriented franchise with a built-in audience and plenty of potential for sequels.
But "Da Vinci," set for release in May, is shaping up as one of the movie world's more complicated exercises - so much so that Sony has dropped a scrim of secrecy over the affair, refusing to discuss anything but the barest details. The script has been closely controlled. Outsiders have been banned from the set. And those associated with the film have had to sign confidentiality agreements.
"There isn't a hidden agenda, there isn't any secrecy, it's just because it's so well known," said Geoffrey Ammer, Sony's president of worldwide marketing, explaining the low profile. "They've got a job to do to make the movie. It was easier for everybody to just go make the movie."
But executives and others connected with the project acknowledge that their silence is also a measure of concern about the potentially incendiary nature of the subject matter. The book, which is fiction, takes aim at central Christian dogma, claiming that Jesus had a child with Mary Magdalene, who was meant to be his true heir. It alleges an enormous coverup by the Roman Catholic Church, which, according to the book, usurped Mary's place in favor of a male-oriented hierarchy that has suppressed what Mr. Brown calls the "sacred feminine."
Even before production began, the studio and the producers Brian Grazer and John Calley received letters from groups like the Catholic League and Opus Dei expressing concern.
The Catholic League asked that Mr. Howard include a disclaimer acknowledging that the movie is fiction. Opus Dei, a conservative Catholic group, was particularly worried about its own depiction, because it is a central villain in the book. "The novel portrays Opus Dei in a completely inaccurate way; if the movie does the same thing it's something we'd be concerned about," Brian Finnerty, a spokesman for the group, said.
Studio officials have consulted with Catholic and other Christian specialists on how they might alter the plot of the novel to avoid offending the devout. In doing so, the studio has been asked to consider such measures as making the central premise - that Jesus had a child with Mary Magdalene - more ambiguous, and removing the name of Opus Dei.
"The question I was asked was, 'Can you give them some things they can do to change it, to make it not offensive to the Christian audience?' " said Barbara Nicolosi, executive director of Act One, an organization that coaches Christians on making it in Hollywood. She said she was approached by Jonathan Bock, a marketing expert hired by Sony for his knowledge of Christian sensibilities, and included in the discussions Amy Welborn, who has published a refutation of "The Da Vinci Code" titled "De-Coding Da Vinci."
"We came up with three things," Ms. Nicolosi said: the more ambiguous approach to the central premise, the removal of Opus Dei and amending errors in the book's description of religious elements in art.
Ms. Welborn said, "If the script took those very strong assertions that Brown makes, and softened them, made them more theoretical rather than bald statements of fact, that might do something."
Mr. Bock declined to comment about his involvement with the picture.
Whether the screenwriter, Mr. Goldsman, has made any of those changes is uncertain, though the studio has publicly hinted that the film is a thriller that will play down religious themes.
But changing the plot of a beloved novel has its own hazards and risks alienating the movie's built-in fan base - those millions of people worldwide who devoured the book and made it, some claim, the most successful book in history after the Bible. (Mr. Brown's agent, Heide Lange, said 36 million copies of "The Da Vinci Code" were in print.)
"There's no way you can take out the central point of the novel, that Jesus married Mary Magdalene and the Catholic Church has done everything in its power, including murdering millions of people, to cover it up," said Carl E. Olson, co-author of "The Da Vinci Hoax," a book refuting the "The Da Vinci Code." He predicted that many devout people would be offended "unless they make a movie that bears a pale resemblance to the book, in which case they'd have a lot of irritated fans."
Mr. Ammer, Sony's marketing president, said the studio would remain true to its source. "My biggest concern is that we make a movie that is entertaining, and that follows as close to the book as possible," he said. "It's not about any particular group, it's about the mass appeal of the book. When you read a good book, you say, 'I hope they don't ruin the movie.' "
Mr. Calley, who was a Sony chairman before becoming a producer, said he considered the film "conservatively anti-Catholic," as opposed to destructively so. "Look at the book," he continued. "Yes, there are clerics that ding it, but there are clerics that are supportive."
Like the novel, Mr. Calley said, the movie can be a tool for discussing the origins of religion, even challenging its basic assumptions, which he said is a good thing. "In our society, most societies, we grow up with our religion given to us by our parents," he said. "We're never truly oriented into the history of it, the subtlety of it. The amazing thing about this book is it's provocative: Is it all true? Isn't it true? As a history book it's extraordinary. As an exploration of the evolution of a particular religion, it's extraordinary."
Mr. Calley was just exiting as chairman of Sony Pictures Entertainment when he made the deal to buy the rights to "The Da Vinci Code" in June 2003. He relied on a longstanding friendship with Michael Rudell, Mr. Brown's lawyer, to corner the rights by offering a pay package that could exceed $5 million once the movie is released, according to people involved.
And though the book is labeled as fiction, Mr. Brown has written and said in interviews that the tale is based on extensive research and historical fact, including a 1982 nonfiction book, "Holy Blood, Holy Grail" by Michael Baigent, Richard Leigh and Henry Lincoln, which Mr. Brown cites as a source.
Many readers are convinced that "The Da Vinci Code" is largely true, though cloaked in fiction. Some fans make pilgrimages to sites mentioned in the book, including the Louvre and the Château de Villette in France and Westminster Abbey in Britain. The movie production has been filming on location in the Louvre and the chateau, but Westminster Abbey declined the producers' request to shoot there, calling the book "theologically unsound."
Among those who take Mr. Brown's revelations seriously is Olivia Hsu Decker, a real estate agent who owns the Château de Villette and lived there during the shoot in June and July. "This book revealed the truth that the Catholics have been hiding for thousands of years," she said in a telephone interview. "The book is fiction, but it's based on truth."
Ms. Decker added, "The book kind of explains to the world how the Catholic Church demonized women such as Mary Magdalene, and also have killed millions of women during the Crusades."
A half-dozen books published in the last two years rebut that very notion, and it is just this attitude that has fueled concern not only among Catholics, but Christian activists of other denominations as well.
"A lot of people are getting their view of Christianity and the Bible from the book," said Alex McFarland, a speaker and writer for Focus on the Family, an evangelical group. He said the message of the book "broke my heart."
In searching for a middle road through this thicket of competing agendas, Sony has opted to say nothing, at least for the moment. And there are signs that the studio has not ruled out attracting religious moviegoers, including those who made an international sensation last year of Mel Gibson's film, "The Passion of the Christ."
"The phrase I heard used several times was 'Passion dollars'; they want to try to get 'The Passion' dollars if they can," said Ms. Nicolosi, referring to her conversations about the film. "They're wrong," she added. "It's sacrilegious, irreligious. They're thinking they can ride the 'Passion' wave with this. And I said, 'Are you kidding me?' "