I kølvandet på kong Uthers pludselige død truer kaos med at opsluge Storbritannien. Når troldmanden Merlin har visioner om en mørk fremtid, installerer han den unge og impulsive Arthur, Uthers ukendte søn og arving, der er opdraget fra fødslen som almindelig. Men Arthurs kolde og ambitiøse halvsøster Morgan vil kæmpe ham til den bitre ende og tilkalde unaturlige kræfter for at gøre krav på kronen i denne episke kamp om kontrol. Disse er faktisk mørke tider for den nye konge, med Guinevere som det eneste skinnende lys i Arthurs hårde verden. Konfronteret med dybe moralske beslutninger og udfordringen med at forene et rige brudt af krig og gennemsyret af bedrag, vil Arthur blive testet ud over fantasi.

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.

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.