This is a prequel.
This is the story of a teenager Alexandria Andros. But it's not the usual story. She is a half-blood. Meaning she is half-human and a half demigod. She is also on the run with her mother. They are avoiding the Covenant but also avoiding the daimons. Daimons are evil creatures who can suck your life away. Literally. They want your aether if you are a pureblood.
When Daimon's attacked Alex may not have a choice, she may need to go back to the Covenant.
A romance is hinted. We know that Alex likes a guy older than she is, his name is Aiden St. Delphi and he is a pureblood.
This prequel is setting the arc. I love every book JA has written so far. So I downloaded the rest of the series at once. I'm sure it won't disappoint me.