Skulduggery Pleasant: Mortal Coil by Derek Landy
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.