The pair discover that the grandfather had inherited Leonardo da Vinci's mantle as the head of a secret society. The society guards the Holy Grail, which is not a chalice but is instead the proof of Jesus and Mary Magdalene's conjugal relationship; Langdon and Neveu must race the killer to find it. Along the way they learn that the church has suppressed 80 early gospels that denied the divinity of Jesus, elevated Mary Magdalene to a leader among the apostles and celebrated the worship of female wisdom and sexuality.

The book portrays Opus Dei, a conservative network of Catholic priests and laity, as a sinister and sadistic sect. In it, an albino Opus Dei monk assassinates four people who guard the secret about the union of Jesus and Mary Magdalene.

The real Opus Dei has posted a lengthy response to "The Da Vinci Code" on its Web site, warning, "It would be irresponsible to form any opinion of Opus Dei based on reading 'The Da Vinci Code.' "

Our Sunday Visitor, the Catholic publishing company, has published a book and a pamphlet offering a Catholic response to the book. The Evangelical Lutheran Church in America has also issued its own guide. One evangelical Christian publisher, Tyndale House, which hit gold with the "Left Behind" books, is about to issue not one but two titles rebutting "The Da Vinci Code."

Several religious groups have published books or pamphlets taking issue with the book.

Though for many readers the notions about Christian history in "The Da Vinci Code" seem new and startling, the novel introduces to a popular audience some of the debates that have gripped scholars of early Christian history for decades.

The academic chatter grew louder after the discovery of the Dead Sea Scrolls in the 1950s and of ancient texts in Nag Hammadi, Egypt, in 1945. Among the findings were early Christian scriptures and fragments not included in the New Testament, including writings that scholars have come to call the "Gospels" of Mary, Peter, Philip, Thomas and Q.

"The Da Vinci Code" floats the notion that the fourth-century Roman emperor Constantine suppressed the earlier gospels for political reasons and imposed the doctrine of the divinity of Christ at the Council of Nicaea in A.D. 325.

A wide spectrum of Christian scholars agree the depiction of the Council of Nicaea is one of the book's most blatant distortions. While there was a diversity of early expressions of Christianity, they agree, Jesus' divinity was part of the church's established canons well before 325 and predates most of the newly found Gnostic and other gospels.

"People were thinking Jesus was divine in some sense or another from the first century on," said Harold W. Attridge, dean of Yale Divinity School and a translator and authority of the Nag Hammadi trove. Attridge, who recently gave a lecture on the novel in California, said that while he welcomed the book as a "teaching opportunity," it "takes facts and gives them a spin that distorts them seriously."

Much of "The Da Vinci Code" scaffolding of conspiracies was constructed in an earlier best seller, "Holy Blood, Holy Grail," published in the 1980s. It relies on a file of documents found in the Bibliotheque Nationale de France that has since been exposed as one man's hoax.

Darrell L. Bock, a professor of New Testament studies at Dallas Theological Seminary, sees "The Da Vinci Code" not merely as an effort to undermine traditional Christian belief but also to "redefine Christianity and the history of Christianity."

"That's why you see so many Christian people react to a novel," said Bock, author of "Breaking the Da Vinci Code."