Foucault's Pendulum, Umberto Eco
Like a lot of people, I am somewhat fascinated and definitely amused by secret societies. My grandmother was in Eastern Star and the Rebekahs. My great uncle was a Mason (or was he just a Shriner?). I'm quite sure I'll be content to be a member of the Leinie's Lodge. Uh, anyway, this is one complex book. As three editors invent a Plan involving every occultic group and idea (Templars, Rosicrucians, alchemy, Jesuits, etc.) they can think of, the Plan seems to take on a life of its own. It's not a quick read, and I found it very enjoyable.