** spoiler alert ** 
 It was a great read, except I had some issues with the conclusion. Not the part about Cassie's mother or the capture of Nightshade, but with leaving out so many other things developed in the novel hanging in the air. 
 After Aaron was killed there should have been a confrontation between Sloane and her father or at least some mention of it. Briggs poisoning and subsequent curing was anti climactic... Done only for the purpose of Cassie facing Nightshade. I feel that if you're gonna poison one of the main characters don't resolve it in the next couple of pages :). 
 Anyway overall, really loved the book and loved the developing mythology of the serial killer cult Naturals are going to face. Honestly can't wait to see how it develops in the following novels!