Q: The Da Vinci Code seems to fit together too well. Is it true? A: No. Both the book and movie are completely fictional.
Any credible research is always backed up by references. Any textbook, research paper, or otherwise factual material always contains a bibliography and citation of sources. Without this, a work is merely the author's opinion and has no basis for truthfulness. Also of note: the front cover of the book, lists it as "A Novel" which means it is a fictional work.
As you will see throughout this FAQ, the Da Vinci Code uses numerous fictional elements, passed off as facts, to lead the reader to a false conclusion of truth. The author does this in a masterful way which gives an illusion that the story is credible.
These fictional elements begin on page 1, where the author lists three facts about: the Priory of Sion, Opus Dei, and secret rituals. All three of these "facts" are in-fact fictional elements that the author uses under the illusion of fact, to begin the novel with credibility. From the very beginning the reader's mind is being set-up or tricked into a false assumption of believability - a very good literary trick indeed.