Sabriel by Garth Nix
A tale of dark secrets, deep love, and dangerous magic!
Since childhood, Sabriel has lived outside the walls of the Old Kingdom, away from the random power of Free Magic, and away from the Dead who refuse to stay dead. But now her father, the Charter-Mage Abhorsen, is missing, and to find him Sabriel must cross back into that world. With Mogget, whose feline form hides a powerful, perhaps malevolent spirit, and Touchstone, a young Charter Mage, Sabriel travels deep into the Old Kingdom. There she confronts an evil that threatens much more than her life—and comes face-to-face with her own hidden destiny.