Riley Sager’s 2026 novel, The Unknown, is a psychological thriller that draws on conventions of Gothic and supernatural horror. Sager is a New York Times best-selling author known for modern thrillers that often pay homage to classic horror films, such as his award-winning debut, Final Girls (2017), and his Reese’s Book Club pick, The Only One Left (2023). In The Unknown, aspiring actress Marin Keane is cast in a horror film about the disappearance of five women from a remote Vermont island in 1926. As part of the director’s immersive method, the cast must spend five days on the supposedly haunted island of New Avalon, living as their characters did. When they’re left stranded without communication, the line between performance and reality blurs as the events of the past begin repeating themselves.

The novel employs a dual-timeline structure to explore its central themes. The 1926 storyline, revealed through historical diary entries, uncovers a past defined by severe psychological distress, illustrating The Persistence of Trauma. This historical narrative is mirrored and manipulated in the contemporary timeline, which explores performative identity and the pursuit of vengeance against exploitation within the film industry. Through its cast of characters, particularly the predatory behavior of the film’s director, the novel critiques Gendered Power Disparities and the Exploitation of Women in Hollywood. As conflicting narratives emerge, from historical journals to faked hauntings and secretly recorded videos, the story constantly interrogates the nature of reality, reinforcing the theme of The Malleability of Truth.

This guide refers to the 2026 Dutton edition.

Content Warning: The source material and guide feature depictions of illness, death, death by suicide, graphic violence, sexual violence and harassment, child sexual abuse, child abuse, emotional abuse, bullying, racism, gender discrimination, mental illness, suicidal ideation, self-harm, and cursing.

Plot Summary

Marin Keane, a struggling New York actress, is unexpectedly cast as a replacement actress in Darkness, a new horror film by acclaimed director Ronan Peters, starring alongside the legendary Violet Wright. The film dramatizes the true story of five women who vanished from a Vermont island called New Avalon in 1926. As part of Ronan’s “method directing” style, the cast must spend five days on the real New Avalon, living as their characters did, without modern technology. Before departing, Marin receives a cryptic text from Lindy Garrett, the actress she replaced, warning her not to go to the island.

On the boat ride with the film’s producer, Loretta Zeverin, the boatman, Pete, tells Marin that his grandfather was the one to report that the original women went missing. Locals still believe that an evil force inhabits the island. On New Avalon, Marin meets her co-stars Violet, Susie Hutchinson, Heather Benchley, and Julianne Brown. She’s subsequently shocked to learn that she’s leading the film as diarist Daisy Rue, the woman whose account is the only evidence of the vanished women’s experience. Her excitement is tempered by the cast’s forced surrender of their phones and Susie’s open jealousy. Marin learns from Loretta that Lindy was fired for refusing to come to the island out of fear, having warned them, “If you go to New Avalon, none of you will leave that island alive” (61).

The group holds a séance as a character-building exercise. After Ronan’s production assistant, Brad, is caught faking ghostly phenomena with fishing line, they attempt a genuine session. The atmosphere shifts as the glass on their makeshift spirit board begins spelling out the names of the actresses’ dead loved ones: Heather’s cousin Clarence; Julianne’s husband, Dean; Violet’s father, Frank; and Marin’s sister, Molly, whose drowning Marin feels responsible for. The séance culminates in terror as the table levitates, the candles extinguish simultaneously, and a disembodied voice whispers a message that only Marin and Susie hear. For Susie, the message is “You will be first” (147); for Marin, it’s “You will be last” (121). The event ends abruptly when Brad collapses in agony. Loretta, who is Violet’s sister, evacuates him on the island’s only boat, taking all the confiscated phones with her and leaving the rest of the group stranded and terrified.

The next morning, the horror escalates when Susie is discovered missing. Her period costume is found hanging high in the branches of a massive oak tree, mimicking the historical disappearances. A search of the island uncovers Susie’s camcorder on a stone slab in a strange clearing. The footage on the camera shows Susie being pursued through the woods at night by an unseen figure before she’s violently attacked. Panic sets in, and the group suspects that Lindy Garrett is stalking them. Their fears intensify the following night when Marin and Heather attempt to signal for help with a flashlight. While Marin is at the dock, Heather vanishes from the shore without a sound; her dress is later found hanging in the same oak tree. Convinced that a supernatural entity, which they call “Azra” after it identified itself during the séance, is responsible, Julianne, Violet, and Marin share stories of sensing the spirits of their dead loved ones. Marin tearfully confesses her guilt over her sister Molly’s death, and they theorize that the entity is impersonating these spirits to lure them to their doom. The pattern continues the next morning when Julianne claims to see her dead husband, runs out into the mist, and disappears, her dress joining the others in the tree.

Now, only Marin, Violet, and Ronan remain. Ronan tries to seduce Marin, kissing her forcibly in the hallway of the main house. She rejects him, and her suspicions about his predatory nature are confirmed. When Marin finds a cell phone that Violet was hiding, she becomes increasingly convinced that she’s behind the disappearances. That night, when Marin thinks she hears the ghost of her sister outside her window, she shines a flashlight and instead finds Susie. She gives chase, and Julianne, Heather, and Violet all appear. Violet confesses that the entire haunting was an elaborate revenge plot. Her secret daughter, Elise Haines, was an aspiring actress whom Ronan filmed during sex without consent. After the video leaked, Elise died by suicide. Violet, Loretta, and the other actresses, all of whom were friends of Elise, staged the events to coerce Ronan into confessing his crimes on a hidden camera. Later, in her cottage, Marin discovers a loose baseboard and finds the five missing pages of Daisy Rue’s diary hidden in the wall. The pages reveal that Daisy had dissociative identity disorder and was the one who murdered the five women. 

Marin agrees to help Violet with her plan to expose Ronan. During a final, secretly recorded séance, during which the plan is to pretend Molly’s ghost is contacting them, Violet instead claims to be possessed by Daisy. Under pressure from the terrifying performance and Marin’s questioning, Ronan confesses to recording Elise and several other women. However, Violet goes beyond the plan. Overcome with rage at his lack of remorse, she stabs Ronan to death with an ice pick. When she “snaps out” of her possessed state, she feigns horror and shock. Now an accomplice, Marin helps Violet throw Ronan’s body off a cliff and dispose of the evidence. 

Later, after finding loose floorboards in her cottage, Marin discovers the skeletal remains of Ruth Hume Semple, a woman mentioned in Daisy’s diary, as well as her journal. It reveals that “Daisy” was an alternate personality of a young woman named Azra Kovacic, who had experienced severe trauma. Her friends on the island—the women who disappeared—were hallucinations; she didn’t actually murder them. However, in a dissociative state, she did kill Ruth, the woman who was trying to treat her. Realizing that Daisy couldn’t have possessed Violet, Marin confronts her. On the dock, as they await Loretta’s return, Violet reveals that there was never going to be a movie. The project was solely a pretext for their revenge. Enraged at being used as a pawn and having her own trauma exploited, Marin reveals that she secretly kept the SD card from the camcorder, which contains footage of the murder. With the power dynamic now flipped, Violet asks what she wants. Marin, no longer an unknown, states her price: “I want […] to be known” (343).

Four years later, Marin is a celebrated actress nominated for an Academy Award. Ronan’s death was ruled an accident, and while Violet got her revenge, Ronan’s public reputation remains intact. Marin leveraged the SD card to launch her career, making a film with Violet that earned her critical acclaim. They share a tense, unspoken pact, forever bound by their secret. While researching, Marin finds a 1931 photograph of a woman identical to the sketch of “Daisy,” who escaped New Avalon and married a Canadian bootlegger. Marin sees a parallel to her own escape from obscurity and a life of being unknown. As the presenter opens the envelope for Best Actress, Marin sits confidently in the front row, having shed her past and finally taken control of her own story.