Agnes and Élise return to find the cat shelter in complete disarray. Cats are running loose, furniture is damaged, and Havelock is disheveled. He complains that the cats are “fiends,” though Banshee sits adoringly by his feet. Realizing the police used Agnes’s arrest as a way to target him, Havelock apologizes and then kisses her. As they discuss the imminent threat of the new bylaw, Havelock proposes fleeing the city. Agnes points out that Élise cannot leave Montréal because of Gabriel. Their conversation is cut short by a strange noise coming from Havelock’s workshop in the basement.

The group enters the workshop, where they confront Valérie, who is holding His Majesty. Valérie reveals that the cat betrayed Agnes by showing her a secret entrance into the warded workshop. Valérie’s apprentices, armed with powerful Artefacts they located using Agnes’s own cataloguing notebook, emerge from the shadows. Valérie uses her magical compass to show that Vortigern’s book is hidden on a floor below the basement workshop. However, Agnes realizes the compass is pointing up, toward the baker’s oven on the main floor; she also remembers that Banshee, who is magic-sensitive, often sleeps near there, confirming her suspicion that the Artefact may be hidden there. Valérie attacks Havelock with a necklace whose pearls transform into burrowing arrowheads; one lodges in his arm and begins burrowing toward his heart before Havelock wrenches it free. As His Majesty lunges at Havelock, Banshee attacks the traitorous cat and chases him away. While the magical battle erupts, Agnes drags Élise upstairs toward the oven.

Inside the baker’s oven, Agnes discovers Vortigern’s book. Its pages are blank, and she realizes its leaking magic is what rewinds time in the oven each night, causing pastries from the past to appear. Using an incantation Havelock once taught her, Agnes activates the book, transporting herself and Élise three years into the past to the night Havelock caused a near-apocalypse.

Agnes explains her plan: She infers she must be the person who took Vortigern’s lantern from Havelock on this night. Thus, she intends to retrieve it. Élise deduces that Agnes wants to save Havelock from Valérie, and concedes to this intention when Agnes asks Élise to trust her.

As they make their way to Mount Royal, Agnes rescues a scrawny black kitten with a deformed leg. From the cover of the woods, they watch as the past version of Havelock fights off attacks from other magicians who hope to kill him and end the magical chaos.

Havelock defeats his attackers, at one point turning an opponent’s magical horse into a giant gift-wrapped box. He then confronts Agnes, hitting Élise with a sleep spell. Agnes retaliates by throwing the rescued kitten at him; the kitten’s claws scratch his face and he trips and falls. Sensing the magic of the time-travel book on her, Havelock mistakes Agnes for Alice Vortigern. Agnes then understands that Havelock recognized her when they first met in the present because he had already encountered her here, in the past. To persuade him to give her Vortigern’s lantern, she tells him he must travel to the Fourth Fathom of the Rivenwood and invent the 12-layer spell of partitioning. Havelock gives her the lantern and departs for the Rivenwood.

As Agnes and the drowsy Élise prepare to return to their own time, Agnes runs into the past version of her deceased husband, Robin. She tells him she misses him before forcing herself to walk away.

Agnes and Élise initially struggle to use Vortigern’s book to return to their own time. The black kitten, however, discovers a “gap” in the spell within the old bakery’s proofing cabinet, creating a portal home. They tumble back into the present-day shelter, and Agnes rushes down to the smoke-filled, chaotic workshop. She gives Vortigern’s lantern to Havelock, who immediately unleashes its power. A great wave of energy erupts from the lantern, washing over the workshop and absorbing all active spells and enchantments. Valérie is left unconscious at Havelock’s feet, and the fighting stops. With the battle over, Havelock pulls a distraught Agnes into his arms to comfort her amid the wreckage.

Yannick returns and confirms that Valérie has slipped away; he is uneasy, since they cannot be certain she is no longer a danger. The lantern has permanently removed the magic of the apprentices Valérie left behind. 

Meanwhile, a large crowd of supporters gathers outside the shelter to protest the anti-magic bylaw, driven by public sympathy stirred in part by Gabriel’s efforts. Élise arrives with the news that the demonstration has succeeded: Faced with overwhelming public support for the shelter, the city council has shelved the bylaw indefinitely. The public, influenced by eyewitness accounts, now sees Havelock as a hero who defended the shelter from Valérie’s attack. Havelock is horrified by his newfound positive reputation, worrying it will ruin his solitary life. With the legal threat gone, Agnes opens the shelter for business to the cheers of the crowd.

Two weeks later, the shelter is thriving, with a waitlist for adoptions and enough donations to plan an expansion. Laurent apologizes and makes amends by adopting the notoriously difficult cat, Ambulance. Agnes officially adopts the elderly cat Thoreau and the black kitten, already named Cataclysm, whom she had brought back from the past. As a gift to the cats, Havelock creates a magical illusion of tropical birds inside the shelter. 

For Agnes, Havelock reveals a more personal gift: He has magically connected the shelter’s attic to an apartment in Paris. He awkwardly invites her to a Parisian café, and she accepts. Havelock climbs out of the attic window and down a fire escape. Tired of being sensible, Agnes decides to follow him, stepping through the portal and down the ladder into Paris.