ASCENDANT by H David Blalock

In the time before the sinking of Atlantis, the government of the southernmost island, Adylonis, is fractured among eight great Houses. Each is a sovereign entity jealous of its power and eager to exercise its ambitions over the rest of the island. However, the greatest city, Moorkai, is ruled by a neutral faction called the University, and the Atlantean Emperor's presence on the island, represented by the priestly order of the Tialsar, maintains the balance of power though esoteric and political maneuvering.
 
House Thran, in exile on the mainland for centuries for its support of the non-human races, the Kel and Telemet, returns to claim its own after Andalarn Thran. Jarl of the House, appeals personally to the Emperor. The Tialsar, who had been in control of House Thran's resources and secular position, are displaced and resent Aldalarn's return.
 
House Suum, blood enemy of House Thran even before the exile, is even more resentful of its return, as the two Houses are traditional opponents in the struggle for the Ascendancy, a title conferred only by the University on the pre-eminent House that equates to King of Adylonis.