A down-on-his-luck inventor turns a broken-down Grand Prix car into a fancy vehicle for his children, and then they go off on a magical fantasy adventure to save their grandfather in a far-off land.
The story of the marriage of England's King Arthur to Guinevere. The plot of illegitimate Mordred to gain the throne and Guinevere's growing attachment to Sir Lancelot, threaten to topple Arthur and destroy his "round table" of knights.