I adored this book, which might be a slightly odd way to describe one's feelings about a book, but Cade was instantly interesting and compelling, Griff the perfect old hand at a very odd game, and Zack grew on me really quickly.
The basic premise is that Cade, a vampire, is sworn by a Blood Oath to defend the President of the United States, which he has been doing for every President since Andrew Jackson. He defends the United States from the things that go bump in the night. Griff is his liaison with the President and Zach is training to be Cade's replacement after an interlude in the Lincoln bedroom with the President's daughter.
Zach's character arc is part of the joy of the book. Seeing if and how they become a team is great. I am eagerly awaiting the next installment. One quick note, if you don't deal well with lots of blood or similar things, you might have to skip parts.