The Deryni series is set in the land of Gwynedd, one of the fictional Eleven Kingdoms. Gwynedd itself is a medieval kingdom similar to those of the British Isles of the 10th and 12th centuries, with a powerful Holy Church (based on the Roman Catholic Church), and a feudal government ruled by a hereditary monarchy. The population of the Eleven Kingdoms includes both humans and Deryni, a race of people with inherent psychic and magical abilities. Throughout the course of the series, relations between humans and Deryni result in ongoing political and religious strife that is often interconnected with the individual lives of the main characters.