Simply put this book is about vampire (reluctant) crusader knights against vampire (eager) Nazis.
Actually it is more subtle than that and more interesting. It did take my a while to get into the book since there were scenes is in the Holy Land in 1291, the Ardennes in 1944, Los Angeles in 1972, and Los Angeles and Europe in current time. Once the book had set things up it got more interesting.
These are a different sort of vampire from those is most fiction, but the story is good.
Not a bad little read if you like vampire and Nazi novels. If you don't care for this genre, you'll probably hate the book. Characters need a little more development, but the overall premise is well thought out.