Secrets of the Witch World — Andre Norton

The Key of the Keplian For time beyond memory, the fire-eyed Keplian horses have lured riders to their death, sating the blood lust of the Dark Tower. All Witch World knows that the hunted, hated beasts serve Evil--all except one young woman. Fleeing her home after her beloved grandfather dies, the orphaned Navajo-Comanche girl Eleeri follows an ancient and magical trail to Witch World. When she discovers the Kepliana mare Tharna and her newborn colt in the hands of men eager to destroy them, Eleeri fights for their freedom. Running for their lives, psychic Eleeri and telepathic Tharna bond. And in a hidden canyon, they discover the awesome truth: The Keplians were created to serve Light, and to ride with humans.

The Magestone

They are two strangers whose people have been at war for a millennium. Mereth, a Dales trader, crosses the sea to Estcarp and the archival citadel at Lormt, seeking clues to the fate of a missing heirloom, an ancient 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