Jaxon’s flashback reveals a childhood memory from 20 years earlier. A young Jaxon, then named Oswald Jackson Jr., is locked in his tiny bedroom by his abusive father. To cope with his claustrophobia, he crawls under his bed, a space that feels safe and chosen. While lying there, he gazes at glow-in-the-dark stars he has stuck on the underside of the bed—his mother found them in the dollar bin, but his father forbade putting them on the ceiling—and escapes into a fantasy world where he’s a starship captain. As his parents fight loudly outside his room, Oswald finds refuge in his imagination.

Back in the present, Jaxon is locked in his room, and the small space triggers his anxiety. He channels his nervous energy into an exhaustive workout with a resistance band. Afterward, feeling calmer, he confronts the typewriter. He reflects on his once-promising career as a sci-fi author, which has devolved into writer’s block and desperation following the cancellation of his trilogy. He recalls a failed attempt to generate publicity by faking a viral photo of a celebrity reading his book.

With no other distractions, Jaxon sits down and finds an unexpected connection between Fletch’s crime novel and his own work. Inspiration strikes, and he begins to write with a fluency he hasn’t experienced in months. Deeply focused, he dimly hears his door open but assumes that it’s Priscilla bringing food. He finishes his sentence and turns to find that the door is closed. A shadow moves behind him, and someone loops his resistance band around his neck, strangling him to death in his chair.

In a flashback from two years earlier, Millie attends her parents’ funeral, unable to perform the grief expected of her. She reflects on her strict religious upbringing and how she has since built a life full of color and creativity, which includes a daily ritual of writing 3,000 words—a compulsion that she feels she can’t safely skip. She recalls lying to her publisher years ago by saying that her parents were dead, a falsehood that has now come true.

Her younger sister, Freya, confronts her for attempting to leave the wake early. Their conversation reveals a deep rift caused by their different upbringings; after Millie left for college, their parents became significantly more lenient, granting Freya a much happier adolescence. Freya criticizes Millie’s YA fantasy novels and her curated online author persona, urging her to mature. Millie coldly retorts that her “dragon porn” is what will now pay for Freya’s life, leaving her sister hurt and stunned.

In the present, Millie is in her room, writing a scene that mirrors the recent events with Jaxon and Malcolm. She internally justifies her accusation against Jaxon, admitting to herself that while she didn’t see him physically push Malcolm, she’s confident in her version of the truth. She remembers having to rewrite her entire ending for Fletch’s novel after realizing that she had written it in the wrong point of view.

A flashback reveals that late the previous night, while intending to deliver her rewritten pages to Rufus’s cottage, she saw Priscilla leaving it instead. Millie confronted Priscilla, accusing her of trying to seduce Rufus to win the competition.

Back in the present, Millie goes to the library for inspiration for a character name. She passes Jaxon’s locked room and calls out to him but gets no answer. On the main staircase, she’s startled by the bloodstain where Sienna died. Kenzo appears with his typewriter and an ax, explaining that he’s moving to the kitchen to feel less isolated. They share a tense exchange.

Millie finds Cate in the library, where they discover how to open the dollhouse. While examining the miniature rooms, Millie notices a network of secret passageways connecting the bedrooms. Later, she joins Priscilla and Kenzo in the kitchen. They decide to bring food to Jaxon, and though Kenzo volunteers to go alone, Millie casually offers to come along.

As they cross the foyer, a gust of wind causes Kenzo to trip and nearly fumble the tray into the antler sculpture; Millie steadies him before any harm is done. They proceed to Jaxon’s room, but he doesn’t answer their knocks. Kenzo uses a key to unlock the door, and they enter. They find Jaxon slumped over his desk, dead, strangled with a resistance band. In shock, Millie drops the tray of food.

Millie is consumed with guilt, believing that her accusation led to Jaxon being murdered. Cate and Priscilla arrive, drawn by the noise. Cate notices that Jaxon’s manuscript pages aren’t on his desk. Kenzo announces that he intends to use the ax to open the safe and retrieve their phones, and leaves despite Millie’s warning about splitting up. While they wait, Cate leans against the wall and accidentally opens a hidden panel, revealing a secret passage that leads directly into Millie’s room.

This discovery immediately casts suspicion on Millie. She denies any involvement, but Priscilla points to a new stack of pages on her desk—her rewritten ending. To prove her innocence, Millie challenges Priscilla to search her suitcase and then runs to Priscilla’s room to search it. There, she finds Jaxon’s stolen pages on the dresser and her own original submitted manuscript hidden under the pillows.

Convinced that Priscilla is the killer, Millie grabs a decorative mace from the wall. She accuses Priscilla of murdering everyone, including Rufus. Priscilla suddenly yells a warning, looking at something behind Millie. Before Millie can react, she’s struck from behind and loses consciousness.

The narrative shifts to Ava Paulson, Fletch’s editor, who has been undercover as the romance writer Priscilla. She watches in horror as Cate strikes the unconscious Millie a second time with a heavy, solid gold book; Millie doesn’t get back up. Ava realizes that Cate is the murderer, a belief bolstered by the fact that she hit Millie twice instead of just once. Trying to save herself, Ava reveals her true identity and her role in organizing the competition, but Cate is unmoved.

Cate reveals that she found the golden book hidden in the foyer floor. She also confesses that her manuscript was generated by an AI program fed with Fletch’s entire body of work; her goal is money, not a writing career. Cate then admits to killing Jaxon; she also admits that she spiked the tea that Sienna drank, although her intent was to put the writers to sleep. She didn’t think Sienna would drink the whole pot, but when she was teetering on the stairs, Cate only had to give her a little push. She also admits to writing the threatening note for Millie and to staying silent while Jaxon was blamed for Malcolm’s accidental fall. Ava is terrified, but she attempts to placate Cate by telling her that they can open the safe and get her devices back. On the way to the safe, Ava finds Kenzo’s body impaled on the antler sculpture downstairs, and Cate confesses that she may have caused his “accident.”

Ava decides to make a run for the small jetty on the other side of the island. Cate pursues her with a crossbow, and she catches up when Ava’s ankle is caught in a snare. Cate comes closer and aims the crossbow. Ava stabs her hand with a pen, causing her to miss. Ava frees herself and escapes in a rowboat, but Cate leaps in after her. Ava hits Cate with an oar, knocking her into the sea. Weighed down by the satchel containing the golden book, Cate refuses to let it go and drowns.

Back at the house, the 72-hour timer on Fletch’s safe reaches 00:00:00. The lock clicks open, revealing the writers’ devices on the shelf—a tablet, a sticker-covered laptop, a smartwatch, two computers with matching screensavers, and an iPhone. The room is empty, and no one is present to retrieve them. Two days later, Eleanor enters the silent house. She calmly collects all the electronic devices from the open safe, places them in her weekender bag, and departs.

Two weeks after the events on Skelbrae, Ava is back in New York, recovering from an ankle injury. She meets with Eleanor, who has adopted Sienna and Malcolm’s dog. Eleanor reveals that she deliberately selected writers with few personal connections, making their disappearances easier to manage, and notes that it shouldn’t be too hard to keep the matter out of the press. Unfazed by the deaths, Eleanor offers Ava a million-dollar deal to ghostwrite the final Fletch novel herself.

Jaded by the publishing industry but tempted by the money, Ava accepts. That night in her apartment, she sits down at her computer to begin writing but finds herself stuck, staring at the cursor blinking after Fletch’s final line: “I should have known” (320).

The narrative summarizes the final outcomes. Ava quit publishing, moved to upstate New York, and found happiness. In a successful marketing move suggested by Holden (formerly Rufus), Merriweather Press released Fletch’s last book unfinished, allowing readers to imagine their own endings. T-shirts bearing the phrase “I SHOULD HAVE KNOWN” became a fashion item among the literati (322), and the book spent 24 weeks on the New York Times Best Sellers list. Holden was promoted to senior editor. Skelbrae is now a tourist destination for his fans.

Kenzo survived his injuries and is at a packed bookstore for the launch of his new horror novel, a fictionalized retelling of the events at Fletch’s house. The book is a major success, and Eleanor is now his agent.

A flashback explains his survival: Cate pushed him down the stairs, and he was impaled on the antler sculpture. He managed to pull himself free and stagger outside. He was found by Angus, whose family originally owned the island and who had stayed on as groundskeeper after selling to Fletch, with Fletch’s promise that the island would revert to him. Angus stitched Kenzo’s wound with fishing line and called for help.

At the book reading, Kenzo gives carefully rehearsed answers during the question-and-answer session, framing his novel as a “what if” scenario inspired by Fletch’s death. He reflects privately on the other writers and the brutal realities of the industry. The event concludes, and he begins signing books for a line of fans so long that he can’t see the end.