The Wizard Hunters: The Fall of Ile-Rien, Paperback/Martha Wells

Once a fertile and prosperous land, Ile-Rien is under attack by the Gardier, a mysterious army whose storm-black airships appear from nowhere to strike without warning. Every weapon in the arsenal of Ile-Rien's revered wizards has proven useless. And now the last hope of a magical realm under siege rests within a child's plaything.