John Boorman directs this epic fantasy drama retelling the legend of King Arthur (Nigel Terry). Years after Merlin (Nicol Williamson) retrieves Excalibur, young Arthur pulls the mythical sword from the stone and is finally recognised as Uther Pendragon (Gabriel Byrne)'s son and heir. Years later, King Arthur builds his legendary castle at Camelot, forms the Round Table and marries Guinevere (Cherie Lunghi), but Merlin foresees trouble in their future.

Meanwhile, Merlin takes on Arthur's half-sister Morgana (Helen Mirren) as his apprentice. After Sir Lancelot (Nicholas Clay) confesses his love for Guinevere, a devasting series of events follows and when Arthur tries to return his kingdom to its former glory by sending his knights on a quest to find the Holy Grail, he faces opposition from Morgana and her powerful allies.