Arthegall and Arthur spend some time enjoying the dead Sultan’s house before deciding it’s time to start traveling again. But Samient persuades them to go see Mercilla, who isn’t far away. Along the way, they hear about a wicked knight named Malengin who steals from travelers and lives far underground, so they decide to try to find him.
Malengin’s lair underground suggests darkness, recalling how the Sultan was just defeated by the light from Arthur’s shield, as well as how monsters like Error in Book I dwelled in the darkness.
Samient leads Arthegall and Arthur to Malengin’s cave. When they arrive, Samient goes first and tries to call him out of the cave. Suddenly, he emerges, and they’re all horrified by his dreadful appearance, such as his empty eyes and long curly hair. He has a staff and a big net—like a fisherman fishes at a stream, Malengin fishes for fools by the side of the road. Malengin ensnares Samient in his net, and Arthegall rushes after her, but the terrain is treacherous, so he sends Talus ahead.
Malengin is perhaps a dark parody of part of the New Testament where Jesus asks his followers to become fishers of men (meaning that they should spread his teachings and make converts). Malengin acts as a disciple for evil, luring fools into his lair, then robbing them.
When Talus catches Malengin, he uses his flail to break his bones and disembowel him. Talus, Arthur, and Arthegall leave him to be eaten by vultures, then free Samient as they continue their journey toward Mercilla.
Malengin is easily defeated by Talus, showing how weak he was when confronted directly. The knights don’t bury him as a sign that he was a wicked man who didn’t deserve respect.
Arthegall, Arthur, and Samient finally make it to the court of the queen Mercilla. Many splendid knights are there to greet them. In the court, there’s also a bad poet with his tongue nailed to a post, as punishment for blasphemy against the queen. The knights greet Queen Mercilla, who also praises Arthur and Arthegall.
The seemingly benevolent court of Queen Mercilla has one surprisingly dark image, with the poet whose tongue has been nailed to a post. While it is possible to read a subversive element into this part of the poem (that Spenser might be secretly criticizing Queen Elizabeth), the more straightforward interpretation is that Mercilla (and by proxy Elizabeth) is such a great queen that it’s a serious sin to blaspheme her.
A woman who looks beautiful but is accused of serious crimes (Duessa) is brought before the court. A man called Zeal stands up and tells of Duessa’s many crimes, including treason against Mercilla. After listing Duessa’s many crimes, Zeal then brings out the hag Ate. He keeps bringing out more women who have committed crimes, including Murder, Sedition, Incontinence, Adultery, and Impiety. Zeal urges the queen to punish Duessa. The queen sees the need for justice but also has pity for Duessa.
It's interesting that Duessa shows up in the court of Mercilla, since earlier in Book I, Duessa was one of the few villains to receive mercy rather than being beheaded. Rather than repent, however, Duessa went right back to her villainous ways. Mercilla’s pity for Duessa suggests the depth of her generosity and contrasts with the more strident calls for justice from others in the court.