Alex Mosher, an imaginative young boy from Brooklyn, New York, finds himself in a precarious situation as he overhears his worried parents discussing their concern over his obsession with writing ominous tales. Struggling with his emotions, Alex lashes out in his room, seizing his collection of "Night books" with the intention of destroying them in the furnace. However, when the elevator unexpectedly halts at a shadowy floor, he stumbles upon an open apartment door where his beloved show, The Lost Boys, flickers on the screen.
Compelled by the sight of untouched pumpkin pie, he indulges and soon collapses, only to awaken in the enchanting residence of a striking witch named Natacha. Here, Alex discovers a closet brimming with clothes belonging to children who were once deemed "not useful" to her. Uncertain of any special attributes he might possess, Alex reluctantly shares his stories, leading to an ultimatum—he must weave a new tale for her each night, or face dire consequences. He meets Yasmin, the housekeeper who was ensnared by Natacha in Washington, D.C., and learns that the apartment that captures them roams the globe, seeking fresh victims and responding solely to Natacha's peculiar keys.
A perilous game unfolds as Natacha insists that Alex end all his stories in despair; if not, the entire apartment trembles with rage. She confronts him about his wish to destroy his works, but Alex skillfully diverts her attention. While exploring the extensive library, he stumbles upon cryptic notes left by another trapped girl—someone he nicknames "Unicorn Girl" due to references of a cherished unicorn necklace she mentions. Forming a bond with Yasmin, they work to earn the trust of Natacha's temperamental cat, Lenore, while uncovering the dark truths behind the fates of past victims turned into figurines in Natacha's cabinet.
As Alex and Yasmin develop their friendship, they discover a recipe for a sleeping potion hidden within Unicorn Girl's notes. After a cunning scheme involving Lenore, they manage to slip the potion into Natacha's perfume bottle, rendering her unconscious long enough to seize her keys and traverse another door, which leads them to a dense and bewildering forest. However, they soon realize they are still trapped within the confines of the apartment.
The adventure takes a treacherous turn when a sinister unicorn lures them toward a mouthwatering gingerbread cottage, but after indulging, they find themselves ensnared again. Alex wakes to a scene of chaos—a room filled with grim skulls and a witch-like figure whose essence is being drained away. The truth unravels as Natacha reveals she was once the Unicorn Girl, who escaped a previous witch that fed on her victims. After using her abilities to subdue that witch, Natacha returned to find her own family gone, compelling her to delve deeper into the dark arts and exploit Alex's creativity for her gains.
In a heart-wrenching moment, Alex shares his painful experiences of feeling alienated and rejected on his birthday—when his supposed best friend, Josh, deemed him "too weird." As the room begins to shake ominously, he realizes the power of his truth, confirming that the friendships he's formed with Yasmin and Lenore have been invaluable amidst the darkness. In a final twist, he gleefully accepts his uniqueness, stating that he is glad he was kidnapped, as it led him to true friendship.
The revelation of a happy ending ignites chaos, awakening the monstrous witch. As a fierce duel ensues, Yasmin seizes the opportunity to snatch Natacha's perfume and escapes with Alex and Lenore. The thrilling chase leads them to Alex's building, where in a moment of bravery, he distracts the pursuing witch and ingeniously renders her incapacitated by luring her into the furnace.
In a heartwarming conclusion, Alex introduces his newfound friends, Yasmin and Lenore, to his ecstatic parents. Yasmin finds her family reunited, and in a future visit, she gifts Alex a beautifully crafted leather-bound notebook with an encouraging inscription: "Stay weird storyteller. Yas." Meanwhile, a dark twist lingers in the air as a figurine among Natacha's collection begins to crackle ominously, heralding the return of Natacha's wickedness with her ominous laughter rippling through the apartment.
