Mortal Coil

"Skulduggery Pleasant and Valkyrie Cain are back - just in time to see their whole world get turned upside-down. While they struggle to protect a known killer from an unstoppable assassin, Valkyrie is on a secret mission of her own. This quest, to prevent her dark and murderous destiny, threatens to take her to the brink of death and beyond. And then the body-snatching Remnants get loose, thousands of twisted souls who possess the living like puppets, and they begin their search for a being powerful enough to lead them. Facing such insurmountable odds, Skulduggery, Valkyrie, Ghastly and Tanith can trust no one. Not even each other."--Website.