Sienna Wood and Malcolm Buchanan, a married writing duo who publish thrillers under the pseudonym Penn Stonely, travel by boat to Skelbrae. Malcolm is seasick but thrilled to be back in his native Scotland, while Sienna contemplates their failing marriage and her private plan to divorce Malcolm, personally and professionally, after the weekend. As they approach the island, they spot a lone figure on the cliffs wearing Arthur Fletch’s trademark wide-brimmed red hat, but they can’t quite make out who it is. At the jetty, they notice a yacht moored there. They disembark and ascend a treacherous path to the main house, a large stone castle.

They’re greeted at the castle’s door by an energetic young woman named Millie Mitchell. Malcolm assumes that Millie is Fletch’s assistant, but she corrects this assumption, introducing herself as a YA fantasy author. She leads them through the grand foyer, pointing out a large gong on the staircase landing and a stained-glass window depicting Fletch’s latest and most famous detective, Julia Petrarch, before taking them to a drawing room to meet the other guests.

In the drawing room, Priscilla Renée Fox, a romance writer, observes the arrival of Sienna and Malcolm. She has already met the other two authors present: Jaxon Knight, a science-fiction writer, and Kenzo Gray, a horror writer. Millie suggests a game to guess each other’s genres, but Kenzo reveals that he has already deduced them all correctly through observation. Priscilla gestures toward a pile of paper on the table and tells Sienna and Malcom that they’ll have to sign non-disclosure agreements—the forms were there when they arrived, and the rest of them have already signed. Sienna and Malcom sign one form, using their shared pseudonym.

Another writer, Cate Newhouse, arrives from the kitchen, having found tea and biscuits for the group. As they wait for their host, the writers discuss Fletch’s famous discipline, noting that his well-known daily writing session, from 10 to 12, is about to end. Just as they wonder when Fletch will appear, a loud gong sounds from the foyer. The entire group leaves the drawing room to investigate.

The writers are met by legendary literary agent Eleanor Vandenberg and a man introduced as Fletch’s editor, Rufus Beaumont. Eleanor shocks the group by announcing that Fletch is dead; he drowned a month earlier. This hasn’t been discovered by the press or his fans yet. Rufus explains that Fletch died before finishing the final Julia Petrarch novel. Eleanor adds that Fletch’s books typically ran close to 100,000 words, but the manuscript he sent her the night before his death stands at 90,000, leaving roughly 10,000 words unwritten.

Eleanor reveals the true purpose of their visit: The writers are there to compete for the chance to ghostwrite the book’s ending. The winner will receive $1 million for completing the book—the remainder of Fletch’s advance—plus another million for a new three-book deal with Merriweather Press. She explains that they were chosen because they’re all “midlist” authors—skilled but not yet commercially famous. In Fletch’s office, all guests are forced to surrender their phones, laptops, and other devices, which are locked in a safe set with a 72-hour timer.

Sienna and Malcolm find their assigned bedroom, which is decorated entirely in yellow and equipped with a yellow typewriter and matching paper for the competition, which Rufus will judge blind. On the desk beside the typewriter sits a bottle of Wite-Out and a printed copy of Fletch’s unfinished manuscript. From the window, Malcolm spots Rufus strolling toward the guest cottage and recalls Eleanor’s rule forbidding any contact with the editor, who will stay in the cottage for the duration.

Sienna and Malcolm argue about their impending divorce. He reminds her of their agreement: She’ll pretend they’re still a happy couple for the weekend in exchange for an amicable split afterward. Malcolm takes a portion of the manuscript to read but quickly falls asleep. Left alone, Sienna begins to read the entire book, titled The Last Gasp.

Jaxon goes for a run around Skelbrae to clear his head, fixating on his professional anxieties after the recent cancellation of his sci-fi trilogy, the Lightspeed Saga, before the third book. He finds a secluded beach and wonders how Fletch could have drowned in such calm water.

Millie appears and playfully flirts with him. Jaxon sweeps her up as if about to toss her into the surf, but his heel catches on a stone, and they both tumble into the frigid sea. As they walk back to the house, cold and wet, Millie asks what he was thinking about on the beach. Hiding his career insecurities, Jaxon feigns confidence and tells her that he was thinking about how he’s going to win the competition.

After finishing the manuscript, which ends on an abrupt cliffhanger, Sienna feels a surge of creative excitement. She goes down to the kitchen for a drink, where she finds Priscilla, Millie, and Cate. They’re soon joined by Jaxon and Kenzo. Sienna shares a brief, friendly conversation with Kenzo, during which he jokes about murdering Jaxon.

When Malcolm arrives, he and Sienna resume their facade as a happy couple. As more writers gather, the group decides to cook vegetarian chili for dinner. Sienna volunteers to chop vegetables.

Kenzo notes that while they prepare dinner, the writers’ different personalities emerge. Priscilla calmly deflects Malcolm’s condescending questions about the romance genre, while Kenzo needles the overbearing Jaxon. Over the meal, Priscilla asks the others their reasons for writing. Their answers lead to a candid discussion about their shared frustrations with the publishing industry and their feelings of being disposable “midlist” authors.

Priscilla defends the value of a good editor, which creates a tense disagreement with Malcolm. Just as the writers seem to be bonding over their shared experiences, Malcolm proposes a toast to Fletch. As the others raise their glasses, Kenzo interrupts, “Sure…if he’s really dead” (80).

Kenzo’s comment shatters the mood, and the writers begin debating what really happened to Fletch. Kenzo theorizes that Fletch faked his death to escape writer’s block, which reminds Sienna and Malcolm of the mysterious figure in the red hat they saw on the cliffs. The conversation then shifts to the possibility that Fletch was murdered.

Jaxon raises Fletch’s golden book as a possible motive, and Priscilla explains the rumor that Fletch had commissioned a priceless volume made of solid gold and jewels to commemorate his success. The writers speculate that thieves killed Fletch while searching for the book and that it could still be hidden somewhere in the house. The energy drains from the group; the writers retreat to their separate rooms.

Unable to sleep, Cate goes to the kitchen for tea. On her way back, she slips into Fletch’s office and tries to open the time-locked safe, guessing that the combination is the publication date of the first Petrarch novel. Her first attempt fails; remembering that Americans put the month first, she tries again, but that attempt also fails. The safe warns that she has only one try left.

A noise in the foyer startles her. She rushes out of the office just in time to see a flash of red as the heavy front door swings shut. Terrified, Cate runs back to her room and locks herself inside. As she tries to calm her nerves, a scream echoes through the silent house.