Sir Lancelot, one of King Arthur's most trusted knights, is suspected of sleeping with Queen Guinevere, the wife of King Arthur. Sir Aggravayne and Sir Mordred conspire to kill him. They are granted permission to confront him by King Arthur.
I'm the king now!
Aggravayne and Mordred enlist the help of 12 knights of the round table They Go to the queen's chambers, where her and LAncelot are. They confront Lancelot who escapes, leaving behind Queen Guinevere. The king punished the queen to death by burning at the stake. Sir Lancelot comes back to save the queen and in the process unknowingly kills Sir Gaheris and Sir Gareth, brother of Sir Gawain, another one of King Arthur's most trusted knights.
Where is King Arthur, I am here to pay my respects to the late Sir Gawain.
King Arthur is dead.
Sir Lancelot and the queen escape. Lancelot's loyalty to the king still remains the same and he is ordered to return Queen Guinevere so he does. Sir Gawain vows to kill Lancelot and avenge his brothers. Gawain and King Arthur go into battle many times with Sir Lancelot, despite Lancelot proving every time that he has the power and armies to overpower them, but he refuses to kill either of them because of his loyalty to the king and the round table.
King Arthur and Sir Gawain are both called away from battle to the coast. In their absence, Sir Modred, the son of King Arthur usurped the throne from his father. Queen Guinevere escaped with some loyal followers to a tower. When King Arthur and Sir Gawain receive this news they come back to battle for the throne.
During the battle, King Arthur and Sir Gawain are both Killed. While dying Sir Gawain realizes he is wrong for holding a grudge against Sir Lancelot and writes to apologize to him. Queen Guinevere gets news of the death of King Arthur and turns into a nun because of both her grief and guilt. Sir Lancelot gets Sir Gawain's letter and returns to pay his respects to him. When he returns he learns of the death of King Arthur.
Lancelot sets out to find Queen Guinevere, and when he finds her she tells him she wishes to never see him again because their selfish love caused the death of the king and the round table. Overcome by grief, Sir Lancelot because a hermit and spends his days praying and fasting. Queen Guinevere dies and the news of this becomes too much for Lancelot to handle and he dies.