This is the Prequel to Half-Blood. It is excellent. It fills you in on what happened right before Half-Blood starts. I didn't read this until after I finished reading Half-Blood, and it was nice to get to see how Alex ended up where she was when the book started. It gives us a little more insight on what the coventant and being a Sentinel mean to her. I also shares a little about her crush on Aiden. I would recommend reading this before, but it is fine to read after as I did.