[CBS News] April 30, 2006--Since it was published three years ago, Dan Brown's "The Da Vinci Code" has become one of the most popular novels of all time, with more than 30 million copies in print worldwide. With a major movie based on the book due out soon, the book seems assured of a place on the bestseller lists for a considerable time to come. What has attracted readers to "The Da Vinci Code" is its central theme, which Dan Brown claims is not fiction but fact — that a mysterious European society, known as the Priory of Sion, has for centuries guarded a momentous secret. That secret, which is the theory at the heart of the novel, is that Jesus Christ married Mary Magdalene and today their descendants are living in France. It's not surprising that this has incurred the wrath of many Christians, including the Vatican, while others have wondered if there might not be some truth to all of this.