The 1996 Oscar-winning film Fargo begins with the following words:
"This is a true story. The events depicted in this film took place in Minnesota in 1987. At the request of the survivors, the names have been changed. Out of respect for the dead, the rest has been told exactly as it occurred."
The film is brilliant, entertaining, absorbing, but complete fiction. The Coen brothers got away with their claim of truth, saying that the film was a work of fiction, and as such the claim to truth at the beginning should also been seen as ficticious. They had used the claim to truth just as a "device" to engage with the audience and have a bit of fun with the naive. The problem was that following on from films like Alive just three years before, audiences were used to seeing films that had been made from the tales of extraordinary true stories and many people, including movie critics, were deceived by the brothers' playful prank.
I read Dan Brown's "The Da Vinci Code" on holiday and knowing more than a little about the book in advance, I immediately thought of Fargo and the Coen brother's device as I read the first word on the first page: "FACT".
Although the book appears in the fiction category, modern readers are accustomed to a type of novel known as "faction". Fictional tales based on historical facts and extensive research into the details of the time. Robert Harris's excellent books: Enigma, and Pompeii fall into this category. Reading such works of faction the reader is both gripped with an exciting tale (usually a thriller) and informed of accurate historical details along the way. "Faction" writers like Harris usually go to great pains to point out and apologise for any discrepancies between their novel and the truth, and make grovelling apologies to the serious historians who helped them write their book.
This is where I see the real problem with "The Da Vinci Code" lies. It is pure fiction dressed up as "faction". By starting with a list of "facts" and claiming that all descriptions of artwork and secret societies are accurate (an entirely spurious claim, as even a modest amount of research will reveal), Dan Brown is making a false connection with readers of faction and making a deceptive claim on the authenticity of the details in his book. Thus even those who do not accept his claim that Jesus married and had children, may go away believing some other distortions about how the canon of scripture was selected, the authority of the gnostic gospels, belief in secret societies and the agendas of Leonardo Da Vinci, Sir Isaac Newton and other great historical figures that have no connection to fact. Defenders of the truth can then be falsely put on the defensive against "evidence" that is no evidence at all.
It seems clear to me that the book has a not so secret agenda. Brown has used the "Fargo Device" to spread the ideas of his anti-christian philosophy to a wide (and gullible) audience.
Fortunately, unlike Fargo, the film (from what I have heard) is very unlikely to win any Oscars!