The Slave War - The Dragonspire Chronicles, #4

Yaz knows where his people are being held. But rescuing hundreds of villagers scattered across the kingdom is no easy task, especially with Carttoom's army hunting you. When some of the more militant slaves start burning farms and killing people, all Hell breaks loose. Meanwhile, The Dark Sages are determined to capture Ariel and enslave her power for their own evil ends. The battle is joined. The Slave War has begun.