Book III, Canto III
None of Glauce’s spells were effective in curing Britomart’s love for the unknown knight, so she devised a plan to consult the source of the mirror. They disguised themselves and traveled to Merlin’s residence, which happened to be in a cave filled with chained spirits. There’s some great information about Merlin’s demise – how he wanted to build a brass wall around his cave, and compelled the spirits to build it for him while he visited his love the Lady of the Lake. Merlin was trapped forever by the Lady, but the spirits kept on building.
At this time in our story, however, Merlin was alive and well. The ladies entered and Glauce tried to lie about their purpose, but it’s pointless to lie to a wizard. “Brusting forth in laughter”, he named them both, and heard Glauce’s plea for more information about the knight in the mirror. Merlin named Arthigall as the Trojan-descended half-brother of Arthur, dwelling in Faery, who is destined with Britomart to found a great dynasty.
What came after that is more or less uninteresting. Merlin gave a long speech about the future of England, basically listing all the monarchs from where II.X left off. I will once again refer you to a helpful list:
The prophecy ended with Elizabeth I.
The women went home and decided to pursue Arthegall themselves. Glauce told Britomart about Angela, the warrior woman of the Saxons, whose armor just happened to be hanging in the castle that night. Britomart stole it for herself, purloining the magic spear of Bladud to go with it. Glauche arrayed herself as Britomart’s squire and off they rode.
The narrative returns to the present with Britomart and Redcross amicably parting ways.