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

The novel begins four months after the conclusion of The Bishop's Heir, and the plot details the continuing efforts of King Kelson Haldane to defeat the combined forces of a political adversary and a fanatical religious enemy.

The novel begins as King Kelson Haldane is making final preparations to launch a military campaign into the province of Meara.

Further complicating matters is the ill-timed return of Kelson's mother, Queen Jehana, whose anti-Deryni sentiments cause considerable friction with her son.

The following day, Kelson sends off the first half of his army, placing it under the command of Bishop Duncan McLain and Earl Dhugal MacArdry.

Shortly thereafter, Kelson and Duke Alaric Morgan lead the second half of the royal army out from Rhemuth to meet the Mearan rebels.

Realizing that Loris is determined to capture him, Duncan orders Dhugal to flee the battle, hoping that the rest of the army will survive.

In Rhemuth, Jehana suffers a crisis of conscience when her own Deryni powers enable her to discover a Torenthi plot to assassinate Nigel.

"[1] In 1986, The King's Justice was ranked 6th in an annual poll of fantasy novels by Locus magazine readers, placing it between Jack Vance's The Green Pearl and Guy Gavriel Kay's The Summer Tree.