Kai is a demon, which means he inhabits the bodies of humans after their death, and has various other powers. He and friends spend the book looking for another friend, which sounds pretty simple, but the world in which this happens has a complex backdrop of peoples, organizations and politics that is gradually revealed during a past and present timeline.

I'd recommend dedicating serious sequential reading blocks vs. the way I did it, which was in shorter snatches, occasionally with a few days in between. It made it hard to keep some minor characters straight and to understand some of the political situations. Do I not know what is going on because it hasn't been revealed yet, or because I forgot? Hard to tell sometimes.