The Da Vinci Code
The Da Vinci Code is a mystery thriller that puts readers through fictional actions used to uncover the truth behind an actual conspiracy theory. It lends from existing materials (e.g. New Testament, Da Vinci artwork, Paganism) to make arguments for the theory whilst the characters uncover it. I remember it being somewhat controversial back when I was in high-school, leading to some sort of Streissand effect taking place. I'm happy to hear that some Catholic groups have taken to using the material in The Da Vinci Code as a launching point for conversation rather than marking it as verboten, which is rarely, if ever, a good idea.
I groaned through some of the symbological analysis by the protagonist and his compatriots, but kept reading because I'm an absolute sucker for any sort of conspiracy/mystery plot above the grade of Scooby-Doo. It's fairly annoying to read this for information given the blend of hard facts and logical leaps, and if you're looking for a history (critical or otherwise) of the Catholic church, definitely continue your reading elsewhere.