It's about a sexy historian (I wonder if he's based on the author...) who becomes embroiled in a conspiracy involving various religious factions. A dying man leaves him the first clue to an ancient mystery which our hero must uncover...
It's not a Great book, but is a rollicking read, even if some of the solutions to the puzzles are a lot less difficult than the characters find them to be. Some of the author's claims are a bit dubious too. I found it to be a bit like a far-fetched action film - I thoroughly enjoyed reading it, but after I'd finished i started to think "Hang on, surely..."