American Kelsie McBlair falls through a gate in an ancient stone ring in the Scottish Highlands while rescuing a wounded wild cat. She and the cat and newborn kittens are besieged on the other side of the Gate by a Dark Rider and a pack of skeletal hounds. When a dying Witch bequeaths her true name and her jewel of power, Kelsie finds herself compelled to take up her sorcerous mission into the heart of Escore, the Green Valley, where magic lies in "trembling balance between the forces of Light and those of the Dark."