The Magestone - Andre Norton

They are two strangers whose people have been at war for a millennium.Mereth, a Dales trader, crosses the sea to Estcarp and the archivalcitadel at Lormt, seeking clues to the fate of a missing heirloom, anancient jewel of Power. At the same time, an Alizonder hound lord, Kasarian, finds that an ancestor's key opens a magic gate to distant Lormt.
Alizonders are wolfish tyrants who fight with sadistic poisons and feedfallen leaders to their dogs, but they have always abhorred the sorceryof Witch World. Now, to Kasarian's horror, a maniacal baron seeks tounleash the dark wizards of Escore — using Mereth's long-lostMagestone, stolen from Kasarian's murdered father!
Two strangers, two foes suddenly share a common cause, and a legacy moredire than either could imagine....