The novel jumps forward to the present day. Marin Keane, a nervous and inexperienced actress, arrives in Vermont after being unexpectedly cast in a horror film by acclaimed director Ronan Peters. The film is a dramatization of the real-life disappearances of five women from an island called New Avalon in 1926, who vanished after supposedly summoning an entity during a séance. 

Before filming begins, the cast must attend a five-day immersive retreat on a remote island, living as their characters did without modern technology. Upon arriving at the dock where she will board the boat that will take her to the island, Marin sees a brunette woman who almost takes a picture of her but looks disappointed upon realizing that Marin isn’t anyone famous. 

During the boat ride, Marin learns a shocking truth from the boatman, Pete: The retreat is taking place on the actual New Avalon, which is supposedly still haunted. Marin’s unease intensifies when she receives a text from the actress she replaced, warning her not to set foot on the island.

Upon arriving at the imposing New Avalon, Marin is filled with apprehension. The producer, Loretta Zeverin, who’s also on the boat, dismisses Marin’s concerns about filming on the island where the women historically vanished. At the dock, Marin meets production assistant Brad Brillstein and, after a moment of intense hesitation, decides that the major career opportunity is worth the risk. Immediately after she steps ashore, Pete departs, and Loretta has her sign a liability waiver and a non-disclosure agreement.

Director Ronan Peters greets her warmly at a small settlement of cottages and a large house. He points out a gnarled oak tree, confirming that it’s where five dresses belonging to each of the women who vanished were discovered. Brad explains that Marin will live in her character’s former cottage for five days without electricity, wearing a single period-appropriate dress. She learns that her co-star, legendary actress Violet Wright, is staying in the main house built by the wealthy Semple family. As she’s led to a table read, Marin wonders why she was hired if the director’s immersive method is designed to make acting unnecessary.

Marin arrives at the main house for the table read and notices strange symbols carved into the building, which Brad speculates are hex signs to ward off evil, attributing them to the Semple family’s superstition. Inside the ornate, dusty parlor, she meets the other cast members: veteran actresses Julianne Brown and Heather Benchley, as well as Susie Hutchinson, a former child star who’s condescending toward Marin. Marin is then starstruck when her idol, Violet Wright, arrives and warmly greets her.

Before the read begins, Ronan and Brad announce that all cast members must surrender their phones and electronic devices for the next five days to authentically experience life on the island. After some protest, Violet agrees, and the others follow suit. Marin receives her script, titled Darkness, and learns that she will be playing a character named Daisy Rue. Believing her role is minor, she’s stunned to see her character’s name on nearly every page. Her shock culminates when she reads the script’s title page, which states that the film is adapted from Daisy’s diary, revealing that she is the movie’s main character.

The novel presents another entry from Daisy Rue’s 1926 diary, set earlier than the entry that opened the novel. Daisy recounts her arrival at New Avalon. After the death of her father, her landlady, who didn’t approve of Daisy’s uncontrollable psychic ability called “the Gift,” introduced her to Ruth Hume Semple. Ruth offered Daisy a place on her island, New Avalon, to learn to control her powers alongside other gifted women, free of charge. 

Upon reaching the island, Daisy senses a foreboding presence, but Ruth reassures her. After settling into her own private cottage, Daisy’s fear gives way to excitement. She meets the other residents: the haughty Katrina Fiske, the bold Jonquil Collins, and the maternal Phoebe Minafer. Despite her initial apprehension about the island, Daisy concludes that she loves New Avalon, feels like she has finally found a home, and never wants to leave.

The narrative returns to the present. Overwhelmed by self-doubt after the table read, Marin tries to get into character by walking in the woods, where she discovers a wall of hex signs carved into the trees surrounding the village. She then overhears her co-stars Susie and Heather and is hurt when Susie suggests that Marin slept with Ronan to get the lead role of Daisy. This prompts Marin to confront Ronan, who reassures her of her talent and reveals that the previous actress playing Daisy, Lindy Garrett, was actually fired by Loretta. 

To help Marin prepare, Ronan secretly gives her a transcript of the real Daisy’s diary. Immediately after, Marin speaks with Loretta, who provides a different story, claiming that she fired Lindy because she was too terrified of the island’s history to participate in the mandatory week-long stay. Loretta concludes by revealing Lindy’s full warning: “If you go to New Avalon, none of you will leave that island alive” (61).

The novel presents another entry from Daisy’s 1926 diary. Feeling watched by Ruth, Daisy goes for a walk in the woods with Jonquil and the antagonistic Katrina; Mrs. Minafer joins them. At the forest’s edge, they discover identical symbols, which Daisy finds unsettling, carved into a perimeter of trees. Deeper within the woods, they find a strange circular clearing containing a large stone slab resembling an altar. Ruth appears, confirming that she was following them, and reveals that the island was previously inhabited by women rumored to have practiced dark arts, speculating that the slab was their altar. She then discloses that her father amassed a fortune manufacturing cannons but later became convinced that he was haunted by the spirits of men killed by his weapons. 

Upon returning to the main house, Daisy points out the same symbol, which Ruth identifies as a witch mark, also called a daisy wheel. She explains that her tormented father carved them all over the island to ward off the evil spirits. Left alone, Daisy feels unsettled, wondering if the marks succeeded in offering any protection.

The novel returns to the present. Alone in her cottage, Marin rereads Daisy’s diary to prepare for her role, noting that Ronan’s screenplay is surprisingly faithful to the historical account. While Daisy’s diary suggests that a supernatural spirit was responsible for the disappearances, Marin is convinced that a real, non-supernatural cause was responsible. 

A persistent scratching sound interrupts Marin’s reading. After the noise stops, she investigates and finds a loose baseboard near the door. Carved into it is a daisy wheel, a protective symbol that she knows from the diary was carved by Daisy herself. Marin recalls that Daisy eventually concluded that the symbol was ineffective.

The novel presents another 1926 journal entry. While wading in the lake on New Avalon, Jonquil prompts the group to discuss their special abilities. Katrina reveals that she has visions of the future, Mrs. Minafer explains that she’s an empath who senses emotions through touch, and Daisy admits that she can hear the voices of the dead. Jonquil expresses skepticism, claiming that she has no such gift. Daisy questions why Ruth has gathered them but hasn’t yet begun to explore their powers. 

As they leave the shore, Katrina appears to have a vision. She describes seeing a dark, inhuman, cloaked figure waiting outside Daisy’s cottage door at night. She quickly dismisses it as a joke to make Daisy look gullible. However, Daisy notices Katrina’s genuine fear, leading her to believe that the frightening vision was real.

In the present, Marin goes to the main house and cooks a meal in the antiquated kitchen, which she shares with Heather, Julianne, and a complaining Susie. Marin mentions hearing a strange scratching sound in her cottage, which visibly concerns the other women. 

Later, Violet appears at Marin’s cottage with homemade martinis, seeking to bond. During their conversation, Violet reveals that Loretta is her sister and that they share a childhood obsession with the New Avalon story. She compliments Marin’s talent, dismisses the other actresses’ gossip as jealousy, and offers career advice about seizing the opportunity the movie is giving her. She admits that she believes something supernatural and vengeful occurred on the island. Violet also reveals that she saw Marin’s audition tape, where Marin told a personal ghost story, and asks if the story was true. Before Marin can fully answer, Ronan arrives, having gathered the other cast members, and announces that it’s time for them to attempt a séance.

In another 1926 diary entry, Daisy finds Ruth inside her cottage with both her journal and suitcase open on the bed. Ruth claims that she’s looking for a hairbrush that she had lost but quickly dismisses the issue and suggests an activity with the other women. They proceed to the main house for an impromptu séance. 

Using an overturned glass and lettered tiles, they make contact with an entity named Azra. The being reveals that it’s communicating from “Hell.” Daisy becomes increasingly frightened as Azra repeatedly spells “Let me out” (98), before addressing her directly by name. When Daisy accuses Katrina of manipulation, Katrina lifts her hands from the glass, which continues moving. A strange, dual-toned voice tells Daisy, “You…will be last” (99). Daisy registers that Katrina heard the voice as well. The séance is violently interrupted when a massive lightning strike cleaves the great oak tree outside. 

Back in her cottage, a terrified Daisy fears that because the session was never properly closed, the malevolent Azra is now loose on the island.

Back in the present, the five actresses gather with Ronan, Loretta, and Brad for a séance designed to replicate the historical one from the script. Using a makeshift spirit board, Marin is pressured into leading the session. After she asks if a spirit is present, the glass on the table moves, and a nearby chair lurches across the floor. 

Marin exposes that the chair movement is a hoax, discovering a fishing line connecting it to Brad’s ankle. Ronan admits that he orchestrated the chair trick and planned other “hauntings” as an immersive acting exercise, while Brad clarifies that the glass moved on its own through the group’s unconscious muscle movements. 

The revelation divides the group; Heather is angry, while Violet and Marin agree to continue for the sake of their roles. Loretta makes the final decision, stating that now that the faked séance is over, she wants to see what happens during a real one.

This interlude consists solely of a three-word declaration. The words “I,” “AM,” and “OUT” are presented sequentially, forming a complete and emphatic statement.