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King Uther banishes his son Arthur; Arthur rescues a boy named Derfel whom he entrusts to Merlin.
An untimely death leads Merlin to locate Arthur and urge him to come back to Britain; chaos ensues when Gundleus assaults Avalon.
Arthur takes Gundleus prisoner, and Nimue begins to plan her revenge; Arthur learns that Gundleus' uncle Gorfydd is preparing for war.
Nimue returns to Avalon, where she is found by Merlin; Derfel and Owain travel to collect taxes from King Cadwys; Gundleus returns to Caer Cadarn.
Derfel feels uncomfortable about the attack on the mine, which Owain keeps a secret; Tristan, prince of Kernow, demands justice for the raid at the mine.
Arthur and the tribe kings enter peace talks; Arthur meets Guinevere, Ceinwyn's lady-in-waiting, while traveling.
Arthur and Guinevere meet secretly before Arthur and Ceinwyn are to be married.
Arthur believes that Bedwin will be able to negotiate peace with Gorfydd; however, when Morgan and Derfel arrive in Powys, they discover a horrific sight.
Gorfydd allies with the Saxons and declares war; Arthur admits he exiled Nimue to the Isle of the Dead.
Derfel finds Nimue inside the Isle of the Dead; guilt-ridden by the deal he's been forced to make with the Saxons, Arthur vows to fight to save Britain.