Tides of Darkness - Avaryan Resplendent, #3

Prince Daros of Han-Gilen is an infamous rake and wastrel-and a hidden and completely untrained mage of enormous power. Caught breaking the strictest laws of the Mageguild and their magical Worldgates, he is sentenced to serve an aged emperor far away from either taverns or temptations. But a tide of darkness is rising to swallow the worlds of the Gates. Mages are dying and worse; but Daros's very lack of training shows him the way to stand against the tide: to enter the darkness, and pay its price, and engage it on its own ground.