This one was fun. Post WWII espionage, academia, mythology, a hint of the occult.....
The mystery is the focus, though it veers a bit into the espionage/thriller. Not much, just a touch.
My only complaint (and this is so much a "I'm cranky on this subject this week" thing) is the ubiquitous "the hero must meet a women and instantly (and mutually) be in love". I'm just over it.
Thankfully, though, this doesn't seem like it's going to be a "new love in every book" kind of series-- the same women is in the next book.
So it's got that going for it.
Plus-- bonus points: Tolkien, CS Lewis, and Ian Fleming are all characters. How can you not love that?
Overall, read it.