The Lost Conspiracy By: Frances Hardinge

This was a science fiction sort of book for children. It was a "Harry Potter" for girls and very cleverly written. The last 40 pages or so seemed to drag, but I still enjoyed it for entertainment purposes. A tribal girl has been raised to be the keeper of her sister, who the tribe is not sure if she is handicapped or special where her spirit can leave her body. The tribal term for this "soul flyer" is "LOST". Mysteriously all of the LOST in this culture are found dead. The protagonist is then not only responsible for her and her sisters safety, but also for unraveling the mystery.