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. These are dark times indeed for the new king, with Guinevere being the only shining light in Arthur's harsh world. Faced with profound moral decisions, and the challenge of uniting a kingdom broken by war and steeped in deception, Arthur will be tested beyond imagination.

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 puts on a feast for King Arthur 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 believes a plan is afoot.

Pursuing the power of her dark magic, Morgan hides in plain sight at Camelot where she begins her plan to drive a wedge between Arthur and his men. Igraine tries to find a way out of Castle Pendragon.

Arthur and his men ride out to defend Bardon Pass after learning of an attack. Merlin comes to the realization that he's been seduced by a shape-shifting Morgan. The men begin to lose faith in Arthur.

Arthur must defend himself against mercenaries on Bardon Pass. Morgan leads Sybil and her followers to Camelot where she receives information that leads her to believe her ambitions will be realized.