The narrator praises mercy, a virtue that Mercilla has in abundance. Duessa is seen as guilty by all in the court and Mercilla regretfully allows her to be executed. Arthur and Arthegall remain in Mercilla’s court for a while.
One day, two young men come to the court to ask for help for their mother, Belgae. Belgae had 17 children, but 12 of them were killed by an evil tyrant named Geryoneo with six arms and six legs. Geryoneo promised to protect Belgae from foreign invaders, but really, he just wanted an excuse to get at her children, whom he sacrifices one by one to a monster he has. Two of the surviving children ask Mercilla for help. Mercilla sends Arthur out to help, while Arthegall goes off on his own separate quest.
Geryoneo represents tyrannical rule. He promises to protect Belgae from foreign invaders while really just eating her children, recalling how real tyrannical leaders often carelessly start wars or commit other atrocities that lead to lots of parents losing children.
Arthur arrives in the land where Belgae lives and sees it has been devastated by its tyrannical ruler. Geryoneo has defiled chapels by building his own false idols near them. The tyrant monster lives in a garrison guarded by many knights. After Arthur dispatches a few of the knights, the remaining guards scatter. Arthur enters the gate, along with Belgae and her two sons.
Geryoneo’s defiling of chapels shows his own ego and lack of reverence. His creation of false idols could be a criticism of Catholics, who use objects like rosaries in prayer in a way that many Protestants find heretical, or at least unnecessary.