Journey into the Void by Margaret Weis, Tracy Hickman (2004, Paperback, Reprint)

After centuries, pure evilfinally has the power -- andthe armies -- to prevail ... Dagnarus has risen from theVoid, backed by an unstoppable horde of bestial minionsand a host of the insidious undead. Mortal kingdom after mortal kingdom must ultimately fall, as traitors wait to crown the dread lord behind the city gates of New Vinnengael. In this time of fear and chaos, the brutal conquest of all Loerem is at hand. Yet hope still flickers dimly in the impossible: in an unlikely hero's courageous venture into the Void's terrible darkness ... and in the reuniting of the long-sundered Sovereign Stone.