High King Uther banishes his son Arthur, who rescues a dying boy named Derfel. Arthur entrusts Derfel to Merlin and Nimue. Years later, Uther has a new heir, but Merlin has a dark vision for the future.

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.

A former warrior now turned monk, tells the story of how Arthur Pendragon became the lord of war.

Derfel feels uncomfortable about the attack on the mine – which Owain is keeping a secret. Nimue is discovered by Merlin who helps heal her. Tristan arrives demanding retribution but Owain denies his guilt.

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 site.

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.