Gawain's brothers Aggravain and Mordred, hating the queen and Launcelot, speak of their adulterous love before numerous knights. Gawain, Gareth, and others ask them to say no more and expect no support from them. Aggravain and Mordred nevertheless inform Arthur, who in fact has known for a long time and has ignored the matter for love of them both. He grudgingly consents to Aggravain's plan to trap them. The jealous brothers spring their trap; Launcelot kills Aggravain with twelve of his knights and wounds Mordred, who flees.
Arthur judges Guinevere to be burned, as law requires. Gawain pleads against it and refuses to have any part in it; his brothers Gareth and Gaheris beg to be excused as executioners or guards. All Launcelot's house urges him to rescue the queen, as he himself desires, and so when the queen is lashed to the stake Launcelot comes, kills all those standing around her-including Gareth and Gaheris, who are unarmed, and takes her with him to Joyous Gard, where Tristram kept Isode until King Mark murdered him.