Half-Blood by Jennifer Armentrout.

Half Blood by Jennifer Armentrout is a breath-taking book that will keep you on the edge of your seat. In this book, Half - Blood Alex is forced back to Covenant, the very place her mother and herself have been running from for three years. But her mother is gone now, murdered by daimons, and she has to go back to the Covenant to try and catch up to the rest of her class, to be a Sentinel. Sentinels are highly-trained fighters, who have spent their entire life learning to fight Daimons, previous Pure-bloods who have turned to the dark side--excuse my star wars reference-- by feasting on aether passed down to pure-bloods and half-bloods from the Greek Gods themselves. But with three years lost, will she be able to catch up, or will she become her biggest fear, a drugged up servant? On top of all this, her trainer is the one boy she hasn't been able to get out of her head since the day she saw him, years ago. Read this book to find out what secrets are in store for Alex!