Kin
Volume 1: Good Neighbors (Hardcover)

Rue Silver's mother has disappeared . . . and her father has been arrested, suspected of killing her. But it's not as straightforward as that. Because Rue is a faerie, like her mother was.

And her father didn't kill her mother -- instead, he broke a promise to Rue's faerie king grandfather, which caused Rue's mother to be flung back to the faerie world. Now Rue must go to save her -- and must also defeat a dark faerie that threatens our very mortal world!