Truth and Fiction in The Da Vinci Code: A Historian Reveals What We Really Know about Jesus, Mary Magdalene, and Constantine - Bart D. Ehrman If you want to get an idea of what early Christianity and Christians were about I'd go with Ehrman's serious works like Lost Christianities: The Battles for Scripture & the Faiths We Never Knew or Misquoting Jesus: The Story Behind Who Changed the Bible & Why.

And he's far too kind to Dan Brown.