Rincewind, Twoflower, and Bethan enter a ransacked, foul-smelling Great Hall. Hearing a crash that suggests the mob has breached the main gates, Rincewind leads the others down to the cellar corridors, following the sound of furious hammering from below.

They trace the noise to a heavily locked door. Rincewind calls out. The responding voice belongs to Lemuel Panter, a former professor who once terrified young Rincewind—and still does. The prisoners identify themselves as the Masters of Wizardry and reluctantly admit they have been locked in without the Octavo.

Stung by the Masters’ low expectations of him, Rincewind declares he’ll open the door himself. He attempts to act magically on the lock, the wood, and the surrounding air in turn, with no result. Just as the wizards inside give up, a faint grinding begins. Through sheer mental exertion that leaves him gray-faced and on his knees, Rincewind forces the lock to turn, and the door swings open.

One wizard that remarks he was slow. A Master named Jiglad Wert explains that Trymon has stolen the Octavo and warns that no single mind can hold all Eight Great Spells. Attempting to do so will shatter Trymon’s mind and tear a hole in the fabric of the universe.

A piercing, unearthly sound erupts from above. The group rushes outside to find the top of the Tower of Art blazing with chaotic light and noise while the sky fills with enormous moons. Wert confirms that Trymon has opened a pathway for entities worse than any conventional demon from the Dungeon Dimensions.

Bethan shames the wizards into action. Twoflower runs toward the tower with a sword before anyone can stop him, Rincewind follows instinctively, and the wizards trudge after. Panter insists Rincewind must join them as the carrier of the eighth Spell. Abruptly, the light and noise from above cease. The Octavo falls from the summit and lands on the stairs, its pages blank. Wert concludes Trymon has successfully read the spells from the book and dismisses the chaos as routine magical side effects. The senior wizards decide to go congratulate Trymon. Rincewind, furious, snatches the book, mentally orders the Spell back onto its page, and shoves the Octavo at Twoflower before storming up the stairs.

At the summit, Rincewind finds the seven senior wizards standing motionless alongside an apparently uninjured Trymon. When Rincewind looks into Trymon’s eyes, he realizes that the Master’s mind has collapsed under the weight of the Seven Spells, and creatures from the Dungeon Dimensions have moved in through the gap. What Rincewind perceives in those empty eyes is not evil but something worse, an indifferent, passionless order that would reshape the universe without noticing or caring about its inhabitants.

Trymon demands the eighth Spell, and Rincewind refuses. Trymon attacks with fire, which Rincewind dodges. Rincewind then confronts the frightened Spell in his own subconscious, asserting bluntly that it’s in his head and will do as he says. When Trymon uses magic to pin Rincewind with crushing pressure, Twoflower appears holding a sword, providing the momentary distraction Rincewind needs.

Rincewind tackles Trymon and fights without technique or fairness, which proves effective against a man who spent his years in libraries rather than exercising. Rincewind is winning when Trymon’s face shifts and the real man surfaces for an instant, crying for help, before the creature takes over entirely. The surroundings transform into a vast arena in the Dungeon Dimensions. Rincewind wounds the entity badly enough that, for the first time in his life, something runs from him, and he pursues it to land a final decisive blow.

Reality snaps back to the tower roof. Rincewind grapples with the monster at the edge of the stairwell opening. Twoflower swings his sword, buries it in the creature, and the thrashing monster rolls off the side of the tower, taking Rincewind with it. The creature strikes the steps far below and explodes in a flash. The freed Spells rise from the wreckage in the form of seven fireballs and fly back into the Octavo.

Rincewind dangles from a stone on the edge of the stairwell and calls up to Twoflower. Twoflower grabs his wrist but isn’t strong enough to pull him up. People carrying torches and shouting begin ascending the stairs below them.

As Rincewind’s grip begins to fail, Twoflower reverses tactics and tells him bluntly to let go and die, which startles Rincewind into holding on. Cohen then arrives at the top of the stairs, having ridden the Luggage to the University, and hauls Rincewind unceremoniously to safety. Cohen reports that the body at the bottom of the tower has reverted to Trymon’s human form and is simply a man broken by the fall. Rincewind discovers that the seven senior wizards have been turned to stone.

Exhausted, Rincewind picks up the Octavo, mentally glares the Spell out of his head, and feels it leave in a flash. The final blank page fills with text. As a crowd reaches the rooftop, Rincewind reads all Eight Great Spells aloud, and the words stream into the air as colored shapes. When Rincewind finishes and closes the book, nothing happens. The crowd turns hostile and surges forward to hurl him off the tower.

Bethan shouts that she knows why the spell failed, and Cohen brandishes his sword to ensure the crowd gives her a chance to speak. She points out one shape in the air is the wrong color, indicating a mispronunciation. Rincewind passes her the Octavo, and they try several pronunciations of the word without success. When Twoflower makes a suggestion about the pronunciation, Rincewind dismisses the idea, but the spell-shape immediately turns a brilliant red. Rincewind pulls everyone back as the Octavo begins to tremble in Bethan’s hands. She drops the book and it floats in the air before erupting in a silent, complex burst of light.

High above, the eight spheres orbiting the red star begin to crack. From each shattered shell a small new sky turtle emerges, each bearing four elephant calves and a new Discworld. Great A’Tuin waits until all eight young turtles have freed themselves, then turns and swims away into space. The turtle’s eight offspring follow.

Twoflower’s first concern after witnessing the hatching is locating his picture box. Great A’Tuin’s contentment radiates outward, briefly placing everyone on the Disc in a state of calm. As the Disc’s own sun rises and the red star dwindles, Rincewind reflects that Twoflower’s way of engaging with beauty by trying to document it rather than reflect upon it is simply his nature.

The calm breaks when the Octavo falls back toward the tower and the crowd surges to seize it. The book drops into the mass of people, but the Luggage snaps it up. Rincewind tells Twoflower the Octavo has secured itself inside, and a scream from the crowd confirms the Luggage is defending its contents. The two slip away and find some drinks.

Twoflower wakes near noon in a hayloft with the Luggage nearby. He finds Rincewind outside the Tower of Art, cheerfully supervising workmen lowering the stone wizards off the roof with the assistance of the University’s Librarian. Rincewind announces his plans to re-enroll at the University. Twoflower then announces he’s going home to the Agatean Empire, explaining that traveling is only meaningful when one has a fixed place to return to and remember from. Rincewind is visibly, quietly dismayed.

Twoflower hires a captain and then gives Rincewind a bag of gold to pass on to Cohen and Bethan, whom Rincewind believes have gone off to get married. Twoflower empties all of his belongings from the Luggage into a sack and then formally tells the Luggage that it now belongs to Rincewind. They say an awkward goodbye, and Twoflower’s ship departs.

On the quayside, Rincewind tells the Luggage he doesn’t want it and kicks it, but he relents when he sees how dejected the Luggage looks. It pads after him as the two head back toward the University. The perspective slowly widens until the Disc is just a glint among the stars.