The Killing Moon by N.K. Jemisin
I LOVE this book. I'm excited for the second book - waiting for it to come into my library.
It's setting is largely based on Ancient Egypt (she talks about this in an "interview" at the end of the book). The magic system revolves around dream-things.
I don't want to spoil anything. I want you to read it. READ IT. It's so good.
Goodbye.