The population of Gwynedd includes both humans and Deryni, a race of people with inherent physic and magical abilities who have been shunned and persecuted for centuries.

At the beginning of the book, Kelson is leading an army into the Duchy of Corwyn to put down the rebellion of an anti-Deryni zealot named Warin de Grey.

Together, they have taken the ducal capital of Coroth and are openly revolting against the Crown due to Kelson's support of his Deryni advisors, Duke Alaric Morgan and Monsignor Duncan McLain.

Meanwhile, in the border city of Cardosa, King Wencit Furstán, the powerful Deryni ruler of the neighboring kingdom of Torenth, seeks to convince Earl Bran Coris of Marley to betray Kelson and assist in an invasion of Gwynedd.

Morgan senses Derry's pain when he attempts to contact him, but his use of his powers is detected by Bishop Arilan, who reveals that he is also Deryni.

During a parley session with the Torenthi invaders, Morgan manages to rescue Derry, but the army is unable to prevent the murder of fifty Gwyneddan soldiers, including Duncan's father.

Though initially reluctant to arbitrate the duel, the Council finally agrees after Arilan brings Kelson, Morgan, and Duncan to confront them.

Lester del Rey found the novel disappointing, saying that "the menaces have all turned into paper dragons" because the author has arbitrarily resolved the story's conflicts rather than working them out.

The other finalists were Susan Cooper's The Dark Is Rising, Poul Anderson's Hrolf Kraki's Saga, and Sanders Anne Laubenthal's Excalibur.