Half-bloods have only two choices in life, become a servant in the house of a pure or kick some Daimons butts.
Daimons are like vampires. They want to drain the Hematoi, they are addicted to the aether.
Alex wants to become a sentinel but in order to do that she will need to prove to her uncle Marcus, who is also the Dean of the Covenant that she can follow the rules. Also she will need help catching up to speed with the other students fighting skills. This is where Aiden St. Delphi comes into play. He is a sentinel, he is pure blood and Alex is totally crushing on him. Only problem is that she can't fall in love with him. Pureblood and Half- bloods don't mix, it's prohibited.
There is an issue with Alex's mom too. Also, not every kid is happy to see Alex back in the Covenant. And there are Daimons looking for her.
Caleb, Alex's best friend, is happy to see her again. They have a great relationship. Caleb is like a brother to her and I love that there is really no triangle with Caleb. But, there is a triangle between Seth and Aiden. Seth is an Apollyon. An Apollyon can control elements too. He is a super bad Half-blood. Has powers and has the respect of the Hematoi. He kills Daimons.
I enjoyed this book tremendously. Love that JA writes great banter. The characters are multi dimensional. I couldn't put this book down. Even though, I love Caleb, Leon is my favorite secondary character.