After the arranged marriage of Arthur (Richard Harris) and Guinevere (Vanessa Redgrave), the king gathers the noble knights of the realm to his Round Table. The dashing and stalwart Lancelot (Franco Nero) joins, but soon finds himself enraptured by the lovely Guinevere. When Arthur's illegitimate son, Mordred (David Hemmings), reappears in the kingdom and outs the secret lovers, Arthur finds himself trapped by his own rules into taking action against his wife and closest friend.