The population of Gwynedd includes both humans and Deryni, a race of people with inherent psychic and magical abilities.

The novel takes place in the early ninth century, beginning ten years after the conclusion of Saint Camber.

The plot of the novel centers on the desperate efforts of the Deryni to protect their futures from a rising tide of human anger and discrimination.

Stunned and amazed by his discovery, Rhys seeks the advice of his father-in-law, Camber MacRorie, the legendary Deryni adept who has been living in the guise of Bishop Alister Cullen for the past decade.

Although equally shocked by Rhys' discovery, Camber is unable to provide any insights, and they soon return to Valoret to tend to the king.

Although Cinhil himself has never truly overcome his distrust of Deryni powers, he has kept the peace between the races throughout his reign, due largely to his close friendship with the man he believes to be Alister Cullen.

However, with Cinhil's death fast approaching, Camber realizes that the ambitious human lords at court will soon be able to wage open war on Deryni throughout the kingdom.

Fearful of the persecutions that will soon be coming against Deryni throughout Gwynedd, Camber suggests a desperate plan to save some of their people.

An attempt to infiltrate the royal court ends in disaster when Earl Davin MacRorie of Culdi, Camber's grandson, is slain while defending the king's brothers.

Rhys convinces Tavis to release him, and immediately attempts to warn Camber that the Regents are planning to attack the cathedral itself.

As he lies bleeding in the snow, Camber ponders his past and his powers, remembering a dangerous spell that may enable him to elude death once again.

Later, as Evaine and Joram gaze at the body of their father, they notice the odd shape of his hands, and they wonder aloud if there might still be a way for Camber MacRorie to live.

In 1982, Camber the Heretic was ranked 6th in an annual poll of fantasy novels by Locus magazine readers, placing it between Robert Stallman's The Captive and F. Paul Wilson's The Keep.

The other finalists for the award were Piers Anthony's Centaur Island, Stephen King's Cujo, F. Paul Wilson's The Keep, and John Crowley's Little, Big.