Roll the Bones (Peter the Wolf, Book 3)

Eighteen-year-old werewolf Peter Holmes saved his sister; for five years, a brutal harpy enslaved and tortured Heather Lupita to feed off her pain. But the monster's price for her freedom is high: Peter must kill a particular vampire--but which one, the harpy won't say. Peter gets his first hint just how hard it's going to be to kill his target when he's forced to face off against a "training opponent," a vampire child who beats him. Worse, other vampires ambush him and leave him close to death. With help from a witch, allies in the FBI, and his own unique abilities, Peter must heal from his wounds, train for his ultimate fight and figure out exactly which vampire he must kill. If he fails, the harpy will take Heather back to spend the rest of her life in unimaginable torture.