In the wake of King Uther's sudden death, chaos threatens to engulf Britain. When the sorcerer Merlin has visions of a dark future, he installs the young and impetuous Arthur, Uther's unknown son and heir, who has been raised from birth as a commoner. But Arthur's cold and ambitious half-sister Morgan will fight him to the bitter end, summoning unnatural forces to claim the crown in this epic battle for control.
When King Uther dies the sorcerer Merlin travels to collect Arthur, a young man he believes can bring an end to the darkness of the land. But Uther’s daughter Morgan sees the crown as her birthright.
Arthur meets Guinevere, the woman of his dreams. Morgan and King Lot conspire to attack Camelot and take the throne. Merlin has Arthur reclaim the legacy sword in the stone to prove his worthiness as king.
Kay and Leontes seek out a trusted new warrior to join them. Arthur and Merlin accept an invitation to join Morgan at her castle for dinner. Arthur is forced to concede defeat in his pursuit of Guinevere.
Merlin sets off on a journey to find a sword suitable for a king by seeking out a legendary sword maker. A conversation with Guinevere changes Arthur and he begins to assert his power by sparring with Leontes.
Arthur creates Camelot's first tribunal of justice which takes shape through a battle of wills, not blood. Aided by Sybil's cunning, Morgan reaches out to the townspeople in her pursuit to take back the throne.
The men of Camelot discover the territory beyond the castle is filled with danger and disorder. Arthur hears Guinevere has ridden out alone to see her father and goes after her to protect her on the journey.
Morgan (EVA GREEN) puts on a feast for King Arthur (JAMIE CAMPBELL BOWER) and his Knights at Castle Pendragon which turns to panic as the castle comes under attack. As Arthur and Morgan’s men join forces to fight, Merlin (JOSEPH FIENNES) believes a plan is afoot.
Pursuing the power of her dark magic, Morgan (EVA GREEN) hides in plain sight at Camelot where she begins her plan to drive a wedge between Arthur (JAMIE CAMPBELL BOWER) and his men. Igraine (CLAIRE FORLANI) tries to find a way out of Castle Pendragon.
Arthur and his men learn of an attack at Bardon Pass and ride out to defend it. Merlin realizes he's been seduced by a shape-shifting Morgan. The men begin to lose faith in Arthur after learning of his betrayal.
Arthur struggles to defend himself against the mercenaries on Bardon Pass. Morgan leads Sybil and her followers to Camelot where she receives information that leads her to believe the throne is within her grasp.