Book excerpt: Marty Volk has a guardian angel. For the past five years, since he was twelve years old, it has saved Marty whenever he’s been in danger. And from a single darkened glimpse one night on the streets of London, he thinks it’s his long-lost sister Rose—ten years older than him, beautiful, intelligent . . . and deceased. For Rose has become a creature of legend that thrives, along with her undead companions, in the shadows of the human world . . . one who tenaciously holds on to her new existence, and who will do anything to survive. . . .