The Harrowing of Gwynedd tells the story of events immediately following the death of Camber, the protagonist of the Camber of Culdi trilogy. The forces of fear and reaction are taking control of the fictional kingdom of Gwynedd during this era. Pogroms against the telepathically gifted Deryni are instituted, laying the foundation for centuries of suppression to come.

The surviving members of Camber's family and circle find themselves faced with two immediate tasks as the novel opens. They must develop tactics and a structure to preserve their race's lore, and save as many Deryni as possible from the savage persecutions. They also have to determine what to do with the saintly Camber's remains. The latter is not as simple a matter as it seems. The very mention of Camber's name is proscribed; the secret of his assumed identity must be kept—and it now appears...