The Nightblade by Matthew Olney
NOTE: I added this book with the correct author, MS Olney, but, of course, BookLikes didn't allow the correct author to be added. They need to fix this problem.
The Nightblade by MS Olney (Matthew Olney) is the first book in The Sundered Crown Saga, I believe, though, I could be wrong.
This story gives some insight to the Nightblades and their mission. This is such an interesting story with great characters. The only problem I had with the story was that I feel as if the ending was rushed a bit, but I would still recommend this book.