As morning breaks over Malbecco's castle, Britomart and Satyrane prepare to leave, but Paridell claims that he must rest there longer to recover from his wounds. Once the other two knights have left, he pursues the real reason he stayed behind: Hellenore. She welcomes his secret love and devises a plan to get rid of her husband and make him look foolish in the process. She sneaks into his store of money and sets it on fire and then goes to Paridell's arms right in front of him; Malbecco is caught between his money and his wife, and he chooses to go put out the fire; in the meantime, the two lovers leave. Miserable, Malbecco goes off in search of his wandering wife. On the way, he meets Braggadocchio and Trompart and offers them money to help him; they slyly refuse the payment and instead advise him to bury his treasure nearby to "keep it safe." Then, the three search through the woods; they soon meet Paridell, who had his way with Hellenore and then abandoned her. They are all too afraid to challenge him for this behavior, and so they continue on in search of the lady. They find her, amazingly, living with a pack of wild satyrs; Braggadocchio and Trompart run in fear of the beats, but Malbecco stays. He tries to convince his wife to come back with him, but she refuses, and he is violently chased off by the satyrs. Outside the woods, he discovers that the two braggarts dug up his money and took off. Miserable, jealous, and grieving, he continues fleeing until he comes to the sea. There he lives the rest of his days consumed by jealous thoughts, until he becomes Jealousy itself.
Meanwhile, Britomart and Satyrane ride away from Malbecco's castle. Suddenly, a young man runs by, who is fleeing a great giant named Ollyphant--the brother of Argante and similarly perverse. Both of the knights chase the giant into the forest and are split up. Britomart is surprised to come upon a man sprawled out on the ground, weeping and wailing. Eventually he explains that he is Scudamore, whose lady Amoret is held captive by an evil sorcerer named Busirane. Britomart vows to save her, if she can; he leads her to Busirane's castle. A wall of flame surrounds it, in place of a moat, and nothing can quench the fire. Britomart, ever fearless, puts her shield before her and walks into the flame; it splits and allows her to pass through. But when Scudamore tries to do the same, he is burned and must wait outside while Britomart enters the castle alone.
Inside, the warrior maiden enters a beautiful room, with walls covered by tapestries of great color and value. These hangings depict "Many faire pourtraits, and many a fair feate, / And all of love, and all of lusty-led (III.xi.29)." They display the love of the gods: the many shapes that Jove took on in order to live with mortal women and many other examples. At the front of the room there is a golden idol on an altar, which looks like Cupid, the god of love. Moving into the next room, Britomart now sees depictions of war and conquest, and the violence that has accompanied love. However, she still sees no persons in the castle; as night falls, she is troubled but stays alert. Suddenly, a trumpet sounds, and a storm rages through the castle. The winds open a door, and as Britomart watches, a long "maske," or procession, comes out of it.
The figures in the maske are the many servants of Cupid, the god of love, who follow wherever his darts fly. There is Desire, Doubt, Fear, Hope, Suspicion, Pleasure, and others--and they all wear an outfit appropriate to their nature. After them there follows a horrible sight: a young woman, with a bleeding wound in her chest, is led out by Despite and Cruelty, who remove her heart and put it in a silver basin. Cupid himself comes out to witness this, riding on a lion; then, the whole procession goes back through the door, which slams shut. Britomart tries to open the door but cannot, so she waits until the next night for the procession to begin again. Indeed, the door swings open again, but when she rushes in she sees none of the figures from the maske. Instead, Amoret is there, tied to a pillar, while the enchanter Busirane cruelly tortures her, opening a wound in her chest. Britomart flies upon him and strikes him down, but she cannot kill him, for Amoret is held to the pillar through his magic. So, with her sword she forces him to remove the spell, freeing the maiden. She leads both of them out of the castle, victorious; the scenes depicted on the walls are now gone, with the dispersal of Busirane's magic. Outside the castle, Amoret and Scudamore are reunited, and the Book ends as they embrace.
Malbecco receives a fate that is appropriate for his jealousy and failure to love his wife: He loses both her and his money and so spends the rest of his life consumed by thoughts of jealousy. That is not all, however; Malbecco is an interesting circumstance of a man being transformed into an allegorical figure. After a time, he "is woxen so deformed, that he has quight / forgot he was a man, and Gealosie is hight [called] (III.xi.60)." He becomes jealousy itself, and, thus, he never really dies. We see the same circumstances in other characters but only after the fact: The huge perversions of Argante and Ollyphante have made them into giant beasts. Seeing the actual transformation within Malbecco shows Spenser's view that vices can consume a man. Malbecco "forgot he was a man"--he let a certain quality possess him and rob him of his identity. All at once, this lends a great deal more credibility to Spenser's allegorical characters; they are not merely symbols or pictures of an abstract ideal, but they are also a very real example of what can happen to a man who has no moderation. Certain physical qualities may be exaggerated, but in characters like Jealousy, we can see the destroyed spirit of a human being beneath the allegory.
These last three cantos bring the Book to a surprising conclusion, at least from the perspective of the plot. After the main character, Britomart, was absent from the story for several cantos, she finally returns to be central to the story in cantos xi & xii. And yet, the action of those two cantos concerns another subplot, the separation of Scudamore and Amoret. The main plot line, Britomart's quest to find Arthegall, is never resolved nor is it even advanced after the first half of the Book. This does not seem to concern Spenser much; what is more important is that the allegory is advanced. Previously, we have seen characters meant to contrast with Britomart--generally a weaker version of chastity (Florimell) or unchecked lust that seeks to remove chastity (Argante, the fisherman, etc).
However, none of these is the true enemy of Chastity as embodied in Britomart, because she is not merely concerned with preserving her maidenhood. Her Chastity is ordered toward Christian love, and so her true enemies are those that seek to destroy love, not just chastity. Her archenemy (in the Book) is Busirane, who (as we can predict from seeing the maske) intends to remove the heart of Amoret; she is wounded in the chest when Britomart finds her, just like the woman in the procession whose heart was then plucked out. The enchanter is no great physical challenge to Britomart, but his sinister intent, strengthened by his magic, is to remove Amoret's capacity to love by removing her heart. In this way, he is a great danger to a champion of Christian love.
Britomart's battle is not won by extraordinary might because her great virtue lies in moderation. She is capable of superlative physical acts but only because her chaste heart is neither too rash nor too timid. This is what allows her to pass through the fire; while Scudamore ran toward it "with greedy will, and envious desire," she passes through in calm confidence (III.xi.25). This is also the meaning of the strange signs she sees in the castle; over every door are written the words, "be bold" -- but over just one door, she sees, "be not too bold." Had she leapt to battle at the first sign of the maske or kept trying to force open the immovable door, she surely would have used up her strength. Instead, she is patient and spends two nights in the castle waiting alertly for the right moment. This patience, combined with powerful action at the appropriate time, gains her an easy victory and brings the allegory of love to a conclusion. True, it is disappointing that we do not see the end of Britomart's own quest; but Book III is more a collection of episodes than a continuous plot. While Britomart is its declared hero it is not necessary for her to reach her ultimate goal within the Book; having witnessed the quality of her patience, we know that she will in the end.