The next arrival is Sir Aglovale, one of the young sons of the late King Pellinore, wearing a black sash for his late mother. Aglovale wants to kill Mordred and Gawaine in vengeance for his brother. Arthur reasons with him; Arthur says that he himself could have punished the brothers but there is no reason to keep up the bloodshed and the feuding. Arthur says he will let Aglovale decide if he wants to kill the brothers but that their lives have been unhappy and they have also lost loved ones in this fight.
Arthur asks Aglovale to not avenge his brother and thus break the cycle of feuding—this refers back to a conversation Arthur had had with Merlyn when he was newly crowned. Merlyn had spoken about the justifications of war and how people must need forget historical feuds to prevent further bloodshed. This is what Arthur is asking of Aglovale—to practice forgiveness and save the need for more violence.
Still undecided, Aglovale proceeds to narrate his adventures. He recounts the tale of his brother Sir Percivale who had been much like Pellinore and whose letter had been found in the hands of their dead sister. Percy had been trying to follow Galahad but was tricked by a witch and found himself in a desert with no horse. After many trials, he finally came across a holy boat intended to take people to the Holy Grail.
Sir Percival is allowed to enter the boat—that will take them to the Holy Grail—because of his innocence and purity. Percival, much like his father Pellinore, is a clumsy bumbling knight. White's depiction of him as that to some extent deflates the idealization of the Grail mythology—Percival is innocent, but he is neither perfect nor perfectly chivalric.
Meanwhile their sister, a nun, received a vision. Galahad was staying at a hermitage not far away; she found him and took him to the holy barge where Percy and Bors were waiting. On the way to Carlisle in the vessel, they were waylaid at a castle where a woman had the measles and could only be cured if she bathed in the blood of a virgin. The knights tried to protect Aglovale's sister but, ultimately, she gave herself up. She asked that her body be sent out to sea in a vessel and that is how Aglovale found her, clutching Percy's letter in her hand.
Aglovale's sister's sacrifice seems somewhat meaningless—it does not aid the knights to find the Grail, and the lady is only suffering from the measles. Her sacrifice is thus simultaneously pious and satiric: the piety is lessened because it seems meaningless and exercised by the sister so quickly and unquestionably.