Refutation of the general heresy of Gnosticism and claims about Mary Magdalene as the wife of Jesus, specifically in response to the forever-running best seller "The DaVinci Code" by Dan Brown (which I rated "Well, OK, I guess" for its fun but not great suspense).
Witherington does a good job of making the theological points in understandable terms. Gnosticism is salvation based on "special knowledge" that not everyone has or understands, and is thus exclusionary. Witherington shows that the claim by Brown (and others) that orthodox Christianity surpressed and branded heretical all teachings they didn't agree with in politically driven councils in AD300-500 is historically incorrect. He shows that in fact a de facto orthodox canon almost identical to the current New Testament had developed for historical (because churches and apostles knew they were true--novel concept--no conspiracy theory required!) and spiritual reasons by around AD125. And this canon did not include Gnostic gospels, in part because most were written after AD125 and were clearly not primary source materials, in addition to their nonhistorical subject matter. The councils that later branded Gnostic gospels heretical didn't exclude them from the canon, but merely ratified the canon already accepted by believers everywhere.
History, or records of action, are important to the gospel. Witherington points out that the word "Evangelion" or "Gospel" in common use meant "something that someone--an emperor or benefactor--had done for them, some sort of undeserved by gracious action." (p. 173) The emphasis was on the action, not the words, in contrast to Gnosticism, with its reliance on special knowledge which would allow you to "save yourself." The "Gospel" was the good news of salvation through the action of Jesus!