Adrift: Dusky Hollows, Book 4 (Unabridged‪)‬

Carrie is spending the summer with her new step-family. Although she's nervous about having a new little sister, Mrs. Huffity warns her that things aren't exactly as they seem. When Carrie stops a group of boys from teasing Shannon, she discovers that something is different about her step-sister. It will be more of a transition than Carrie ever expected. After all, her step-sister isn't human.