Most of the knights then set out separately on Grail Quest. During the Quest, Launcelot, Percival, and Bors experience deep religious conversion, while Ector and Gawain are told by a hermit that they are not pure enough to achieve the Grail Quest. Galahad, Percival, and Bors meet up and continue the Grail Quest, but they are briefly parted. Launcelot and Galahad continue to the Grail at Castle Corbenic, where Launcelot is shown to be unworthy of the Quest. When Sir Evelake dies after his embrace with Galahad, Galahad is identified as the knight who will achieve the Grail Quest. Galahad is made a king who dies shortly thereafter, while Percival becomes a hermit. Bors returns to King Arthur's court.
Launcelot also returns to the court and continues his love for Guinevere. After a series of trials, Guinevere is convinced of Launcelot's love for her. Although Arthur knows of the affair and overlooks it, he is prompted by Aggravain and Mordred (Arthur's son by Lot's wife) to take action; Guinevere is sentenced to be burned at the stake. Launcelot rescues her and takes her to his castle, Joyous Gard, but in the battle, Launcelot kills Gareth and Gaheris, who are at the execution but are unarmed. Launcelot returns Guinevere to Arthur, but Launcelot is banished, along with his followers. Gawain swears vengeance for the death of his brothers and insists that Arthur attack Launcelot. Arthur agrees, but while Arthur and Gawain are away, Mordred makes himself King of England, claims Guinevere as his wife, and attacks Arthur's army. Gawain is mortally wounded and warns Arthur in a dream not to continue the battle. Through a misunderstanding, however, the battle continues; Arthur kills Mordred but is mortally wounded by him, as Merlin has prophesied.
Launcelot and Guinevere both die of illness soon after, and Constantine becomes king. The Round Table is disbursed.
