Excerpted from the forthcoming The Gospel Code: Novel Claims About Jesus, Mary Magdalene and Da Vinci with permission of Intervarsity Press.

On the surface of things, all seems well. You pick up a copy of Dan Brown's bestseller The Da Vinci Code. What could be more fun than reading a real page turner? This books captures your attention and holds it as well as any John Grisham novel.

Yet for those who have been reading sensational claims about early Christianity over the years, there is something strangely familiar about this book. Wasn't there a book very much like this one published some twenty years ago? It was entitled Holy Blood, Holy Grail and it came out in 1982. Or consider the 1993 book written by a woman who says that reading Holy Blood, Holy Grail changed her life-Margaret Starbird's The Woman with the Alabaster Jar: Mary Magdalen and the Holy Grail. In this book Starbird is reacting to what she sees as the repression and exclusion of women in the Roman Catholic tradition. Unfortunately, what she offers us is a story of Mary Magdalene (who she wrongly identifies with Mary of Bethany, who anointed Jesus). According to Starbird, Mary Magdalene was Jesus' wife, and she became the Holy Grail in the sense of bearing Jesus' children and passing along the holy blood. Ultimately Starbird relies more on medieval lore and art, and fails to take the Bible seriously.

There was a tendency in medieval exegesis, beginning with Gregory the Great, to identify Mary Magdalene with the sinful woman of Luke 7:36-50 and sometimes also with Mary of Bethany. We will deal with the former mistake shortly, but here it needs to be noted that a woman who is identified as from Magdala (Mary Magdalene) cannot be identified at the same time and in the same Gospel as from Bethany (see John 12:1-3 and John 19:25). Geographical designations were used in a fixed way to say where a person was from, not where they might be currently living. This was done because it was believed that a person's origin said something definitive about (and sometimes even determined) who that person was or could be, hence the question of Nathaniel about whether anything good could come out of Nazareth (John 1:46). In that culture, geography, gender and generation (parentage) were thought to determine identity and personality.

In a culture where there were no last names, a geographical designation was one of the main ways to distinguish people with the same first name, and it appears the geographical designation was regularly used of those who never married, especially women who could not use the patronymic ("son of ...": as in Simon bar-Jonah, which means "Simon, the son of John"). In the Greek New Testament, for example, in Luke 8:1-3 Joanna is identified by the phrase "of Chuza," which surely means "wife of Chuza," but in the same list Mary is said to be "of Magdala." Had Mary of Magdala been married to Jesus, she would have been identified in the same way as Joanna, not with the geographical designation.

Once Holy Blood, Holy Grail and The Woman with the Alabaster Jar are examined and we turn to The Da Vinci Code, we realize we've been down this road before-twice! Only now it's being served up in a novel that purports to be based on the facts unearthed by Baigent, Lincoln, Leigh, Starbird and others. Lest we think that Dan Brown intends for his book to be seen as pure fiction, we are told on the very first page of his work, titled FACT, that not only is there a Priory of Sion and a Catholic sect known as Opus Dei, but "all descriptions of artwork, architecture, documents, and secret rituals in this novel are accurate."

Our concern isn't so much with Brown's ability to describe art or architecture accurately (though we will question his interpretation of da Vinci's famous painting of the Last Supper), but rather with his handling of ancient documents and his treatment of early Christian history. In these realms he is not merely out of his depth, he is also a purveyor of errors of both fact and interpretation, including some mistakes that even the most amateur student of religious history should never make.

He can't hide behind the disclaimer that "this is fiction" because his very first page intends to give the impression that it is a novel grounded solidly in history. He presents his work as historical fiction: though the main characters and their drama are fictional, the materials they are seeking and studying are portrayed as facts or at least probably true.

There should have been a caveat emptor-"let the buyer beware"-on page one.