Lords of Existence - Saga of the God-Touched Mage, #8

Ultimate power. Treachery. A battlefield of pure magic. Garrick has destroyed a god-like planewalker, and now finds himself shunned by his superior and marked for death by the Lords of Existence. He also discovers his powers have grown to monstrous proportions, and realizes that if he loses control now he may well destroy all life in Dorfort, and perhaps even across the entire plane of Adruin. As Garrick retreats to a sanctuary deep inside the ruins of the underground city of Arderveer, the Lectodinian order seizes the opportunity to unleash their plans to storm the plane.
Meanwhile, the ruling powers of Existence decide that the easiest way to punish Garrick is to exterminate Adruin. In Lords of Existence Garrick confronts his own humanity, his banished superior, and human leaders who refuse to see the truth as he takes his fight against the planewalkers all the way into the world of All of Existence itself. To win he may have to make the ultimate sacrifice, and every life in Adruin hangs in the balance.