Dan Brown's mega-popular "DaVinci Code" is an OK read that posits a sinister role for the Catholic Church and the Knights Templar over the last 17 centuries. The book is supposedly well-researched, and seems so possible . . . until Brown stumbles on a basic tenet of Catholic faith. The book then starts to appear sloppy, as well as being anti-Catholic to the core.
Among Brown's big mistakes is a misunderstanding of The Immaculate Conception. Brown has a serious religious scholar wrongly describing the Immaculate Conception as the miraculous implantation of the sinless Jesus in Mary's womb . . . but it is not. The Immaculate Conception -- as anyone who as ever take one religious class in college can tell you -- refers to the miraculous implantation of the sinless Mary in her mother's womb.
Dan Brown wrote a fun, readable yarn in this one . . . but keep in mind the mistakes. Despite what the author seems to be claiming, it is fiction.