HarperCollins Publishers Dying of the Light

Hes dead. Shes deadly. The bad guys dont stand a chance. The ninth book in the bestselling Skulduggery Pleasant series. Following the loss of Valkyrie Cain, Skulduggery Pleasant must track down Darquesse before she turns the world into a charred, lifeless cinder and so he draws together a team of soldiers, monster hunters, criminals and Valkyries now murderous reflection. Not everyone gets out of this alive. A thoroughly satisfying blend of humour, magic and adventure Rick Riordan, author of the Percy Jackson series