It is a week later and the Gawaine clan waits in the justice room. Outside in the courtyard, a pyre is being readied to burn the Queen to death. Mordred is with the brothers, with his arm in a sling. It appears Lancelot killed all the knights outside his bedchamber, apart from Mordred. Quietly, the King enters, looking tired. Mordred is crying because his brothers have been calling him a coward (they think he survived only because he fled). Arthur explains that he had asked Lancelot not to kill his son.
Arthur has been put in a terrible position—because of his new laws, Guenever must be executed after being found guilty of treason. Arthur has worked all his life to promote justice and to ensure it is upheld; yet, he simultaneously hopes that Lancelot will rescue her and by doing so prevent justice from being carried out.
Mordred announces that Lancelot will try and rescue the Queen; Arthur tells him he has made the guard as strong as he can. But Mordred disagrees, saying that Arthur has left off some of his strongest knights. Arthur asks Gareth and Gaheris to join the guard; they refuse to go armed against two people they love, but say they will go unarmed.
Mordred knows that Arthur must abide by his own justice and thus when Mordred says the guard is not strong enough, Arthur must add more guards to show he is not trying to prevent justice from being served. Gareth and Gaheris also believe in and follow Arthur's system of justice, but refuse to actually do violence in defense of a system that is being manipulated to create unnecessary cruelty. In a way, Gareth and Gaheris are the ideals of the knights whom Arthur wished to create with his new order.
Mordred leaves, and Gawaine and Arthur turn to watch the Queen's execution from the window. Arthur hopes that Lancelot will come. The Queen is brought out in a white shift; they pray. Suddenly there is a loud bugle and the court is filled with the charge of many cavalrymen. It is Lancelot! He fights his way to the Queen, takes her from the podium and flees with her on his horse.
Lancelot, as both Arthur and Gawaine had prayed, does rescue Guenever. However, because of the number of guards Arthur had placed around Guenever to prevent her being rescued, many are killed.
Arthur and Gawaine embrace and then call the page for some wine to celebrate. Mordred, unarmed and ghostly, enters the room. He says that it is carnage, and that Gareth and Gaheris are among those slain by Lancelot. They refuse to believe it—Lancelot loved Gareth and besides he would never slay two knights who were unarmed. Gawaine stumbles away, sobbing, to see if it is true. He returns crying "It is true!" and falls at Arthur's feet.
The deaths of Gareth and Gaheris are tragic and immensely divisive. They were unarmed—under knightly law, it is unheard of to slay a knight unarmed. Yet Lancelot—who is Arthur's best knight and who supports Arthur's ideas—has slain them both. Their deaths are deeply ironic and herald the beginning of the Round Table's collapse.