Kara is a Summoner. She is able to see the arcane, magic, Otherworld (whatever you want to call it). She is also a homicide detective. Ryan and Zack are FBI agents that are aware of the arcane. But, they both have secrets. Rhyzkahl is the demon that has a pact/contract with Kara; she has to Summon her once per month. His motives are also unclear.
I enjoyed this world. I especially like that the demons are from another dimension and religion has absolutely nothing to do with it. Great mix of the paranormal and detective/mystery elements. The Big Bad(s) are not easily guessed. Now for some answers regarding the boys (Ryan and Zack). This book finally had some......but more questions came with those answers. I would like to see Eilahn in the next book too. She was an interesting addition.