This was such a great intro to a new world. I don't even think I understand everything at this point and how it all works, but I'll try to explain without giving any spoilers. There are different groups in the world. There are Psy people who seem to be able to do things with their brains. They are all connected to a hive-mind kind of thing, but they have privacy and can even cloak themselves if they want. However, they can't live without the connectedness of the others, so they can't leave the hive without dying. There is a council that governs them and seems to run things.
Then there are regular humans... no need to explain them. :)
Then there are changelings. They are shifters. I know there are leopards, wolves, and others, but I don't know a ton about them. They live in kind of packs and have alphas who run things. They make alliances with each other in certain circumstances, or they fight with each other if they've been wronged.
This book is about a serial killer who is killing changelings, and the changelings thinks the killer is a psy. They enter into an agreement with a powerful Psy so that they can try to use her to find out who the killer is and why they are hiding the killer in the hive.
It's a really good book that seems to have the world and Sascha's story as the main plot and the romance as the secondary plot. I loved it and am moving right into the next book.