Witch — Donald E. McQuinn

Rose Priestess Sylah's successful quest for ancient knowledge had shattered the unity of the Church and branded her a witch. Her only protection, and the only hope for a better future, lay with Gan Moondark, ruler of the united Three Territories. But Gan's fledgling empire was beset by enemies on all sides: Church wanted to reassert her traditional control and suppress the knowledge revealed by Sylah's quest. The heretic religion called Moondance was sweeping across the land, unstoppable, and its goal was the utter destruction of Gan and Sylah. And the deadly coastal raiders called the Skan were banding together with both Church and Moondance against Gan and Sylah in the hope of a rich plunder of slaves taken from Gan's lands.
As the winter set in, Gan had but months to plan for the defense of his people. And so once again he turned to the strangers--resurrectees from the twentieth century--who had helped him found his empire, for it was only with the technology of a long-dead civilization that Gan could hope to overcome the forces arrayed against him. But the skills and knowledge that the strangers possessed were feared even by Gan's supporters--and if his people began to believe that the strangers practiced dark magic, Gan's campaign for freedom would be doomed from the start...