Camille Preaker works as a reporter at the Daily Post, an unremarkable newspaper in Chicago. When Camille’s boss, Frank Curry, sends her to her hometown of Wind Gap, Missouri, to investigate the second missing girl there in less than a year, she is reluctant to return—the withdrawn, heavy-drinking Camille holds within her a wealth of trauma and pain related to the death of her younger sister Marian years ago. When Camille arrives, she pays a visit to the closed-off sheriff Chief Vickery, who is reluctant to talk about either case. After prodding the man, Camille learns that last year, nine-year-old Ann Nash was found strangled to death in a creek in the woods, with all of the teeth pulled from her mouth—now, ten-year-old Natalie Keene is missing, too. Camille pays a visit to her mother’s house and asks to stay there for the duration of her assignment. Camille’s family is Wind Gap royalty—her mother, Adora Crellin, is the heiress to a hog farm which produces two percent of the country’s pork. Camille asks Adora where her thirteen-year-old daughter Amma is, and Adora says that she’s upstairs sleeping. Camille sleeps fitfully and wakes up before dawn to head down to the police station. When Camille arrives downtown, she stumbles upon a horrific scene: Natalie Keene’s body has been propped up on the street, and all of her teeth are missing from her mouth.
The day after Natalie’s funeral, Camille goes downstairs to find her half-sister sitting on the porch playing with a four-foot dollhouse, an exact replica of Adora’s sprawling Victorian manse. Though thirteen years old, with the blossoming body of a young woman, Amma is dressed like a young child. Camille realizes that she has seen Amma around town over the last several days with a gaggle of girls—always dressed provocatively and behaving strangely. Amma explains that when she’s home, she’s Adora’s “doll”—when she’s with her friends, she’s “other things.”
Downtown, Camille manages to talk to Vickery, but the two are quickly interrupted by Richard Willis, a detective from Kansas City who has been sent to investigate the murders. When Camille returns home, she undresses and looks over her own ruined body—she is a cutter who has scarred hundreds of words into every surface of her skin, save for her face and neck and the center of her back. Camille began cutting when she was thirteen and continues to feel her skin “scream” at her in moments of stress. The next day, Camille runs into Richard again, and the two strike up a deal. He asks Camille to help him understand Wind Gap’s violent history. In exchange, he offers to help Camille with her reportage. On her way home, Camille encounters Amma and her friends stealing flowers and gifts from where Natalie’s body was found.
The following day, Camille runs into a group of her mother’s friends at a restaurant. The women invite Camille to sit with them, and she overhears their gossip about the person the women suspect might be the murderer: John Keene, Natalie’s teenage brother. A drunken Jackie warns Camille that Adora has been acting strangely lately. Camille then heads over to the Nash home to question Ann’s parents, Bob and Betsy, about their daughter, whom they describe as headstrong and fierce before revealing to Camille that Adora was tutoring both Natalie and Ann in spelling. On the way home, Camille spots Amma putting around town in a golf cart. She follows Amma all the way out east to the hog farm, where she watches in horror as Amma sits down in front of a nursing pig and squirms with delight as the sow’s piglets fight over her bloody nipples. The following day, Camille tries to question Natalie’s mother, but is thrown out of the house when Mrs. Keene realizes that Camille is a reporter. John Keene’s girlfriend, Meredith Wheeler, is driving past at that moment and offers to have John to talk to Camille.
Meredith and John show up at Adora’s house to talk with Camille. Over the course of their conversation, it emerges that John doesn’t have an alibi for the night Natalie was killed, and Meredith—a popular cheerleader obsessed with her own image—is desperate to clear John’s name. Camille has heard about both Ann and Natalie’s headstrong personalities; John admits that he and his family moved to Wind Gap from Philadelphia after Natalie attacked a classmate with scissors, blinding her in one eye.
Camille and Richard spend the following day driving around together, and the two share a kiss. That evening, when Camille returns home, Adora is waiting for her downstairs, seemingly drunk. Adora confesses that she never loved Camille, and wishes it were Camille, not Marian, who had gotten sick and died. The next morning, Camille interviews Meredith, who reveals that Ann and Natalie were both biters—Natalie bit Meredith twice, and Ann even bit Adora. Camille meets up with Richard and asks whether he believes a man or a woman committed the murders. Richard says he thinks a man is responsible for the crimes—a woman couldn’t have committed such abject violence. Camille reveals that she has learned that Ann and Natalie were violent biters, but when she refuses divulge who they bit, or why, Richard accuses Camille of stringing him along and leaves. The next day, Camille goes over to Richard’s apartment to apologize. The two have sex—though Camille insists on keeping her clothes on to hide her scars. Later, Camille goes to a party with Amma and her friends. Amma gives Camille OxyContin and Ecstasy, and soon the two are tripping hard. That night, Camille allows Amma to fall asleep in her bed, but Camille has a dream in which Marian appears to her and tells her that it’s not safe in Adora’s house. In the morning, Camille wakes up feeling awful. Adora comes into the bedroom and feeds her a blue pill. In a haze, Camille heads down the hall to Amma’s room—Amma is sitting naked on the floor in front of her dollhouse, and after confirming that Adora gave Camille the “blue,” warns Camille about what’s to come. Camille realizes that Adora poisoned Marian to death—and is now doing the same to Amma. Camille rushes to Jackie’s; Jackie admits that she always suspected Adora’s responsibility for Marian’s death, and urges Camille to leave town. Camille, still terrified of going back home, drives out to a bar on the edge of town. There, she finds a very drunk John Keene, who begs her to believe that he is innocent. Camille knows what it is like to lose a sister, and promises John she believes him. The two head to a motel together, where John and Camille have sex—John glimpses one of Camille’s scars and demands to see them all, and she allows him to become the first man in fourteen years to see her naked body. In the morning, Richard and Vickery knock on the motel door—Adora called the police to report that Camille hadn’t come home. Richard is shocked and dismayed to find Camille with John and refuses to accept her apology. Camille visits her old high school friend Katie, who was an aide at Ann and Natalie’s school. Katie reveals that Amma was particularly awful to Ann and Natalie.
Camille finally goes home, and Adora offers her a large glass of bluish milk. Camille decides to take her mother’s medicine again to prove to herself that she isn’t crazy. Twenty minutes later, Camille begins vomiting. She rushes to the nearest hospital, where she demands to see Marian’s old files. In them, she finds a note from a nurse who suspected Adora of Munchausen by Proxy syndrome—a condition in which a caregiver, usually a mother, inflicts illness upon another in order to gain attention and sympathy. Due to Adora’s status in Wind Gap, the nurse was unable to convince anyone else to speak up. The distraught Camille stops at a payphone and makes a call to Curry, in which she confesses that she believes her mother killed Marian, Ann, and Natalie. After hanging up, Camille tracks Richard down at a local restaurant and accuses him of suspecting Adora all along. Richard says that he has obtained a search warrant and will be coming by tomorrow. Camille returns home, and Adora invites Camille up to her bedroom—a room Camille has long been forbidden from entering. As Camille enters, she marvels at the exquisite ivory floors. Adora invites Camille into bed with her and fixes her a drink, apologizing for not loving her. Camille swallows the drink and tells Adora that she will never forgive her for what she did to Marian.
Camille wakes up feeling fevered and weak, covered in her own sweat and urine. Adora helps Camille into the bathtub and feeds her more pills and blue milk. Camille’s thoughts begin to blur, and she falls asleep in the tub—she is awoken by screams sometime later, just as Richard bursts in through the door. He tells Camille that everyone needs to get out of the house and offers to take her to the doctor for testing. That evening, police find an exhaustive array of industrial-grade laxatives and emetics, illegal antibiotics, and horse tranquilizers in Adora’s room—every single medication is found in Camille’s toxicology test. Police also uncover a diary in which Adora details her “treatments” of Marian and admits to killing her when she “couldn’t stop” making her ill. The police also find a pair of pliers in Adora’s room, trace amounts of blood found on which belong to both Ann and Natalie. Adora is arrested for the murders, and Camille takes custody of Amma, bringing her back to Chicago to live with her.
Amma proves an exhausting charge—she is nervous, needy, and obsessed with female killers. She rejects therapy and demands that Camille buy her expensive furnishings for her dollhouse. As time goes by, Amma makes a friend at school, Lily, who comes over often. One night, Camille wakes up to find Amma standing over her, feverish and sweating, accusing her of liking Lily better. Amma then asks for Camille to care for her like Adora did—when Camille says they won’t do things Adora’s way, Amma sobs.
A few months later, Lily disappears on her way home from school, and is found dead a few blocks from Camille’s apartment—with six teeth missing. Camille finds the teeth in Amma’s dollhouse and realizes that Amma was using the teeth pulled from her victims’ mouths to recreate the ivory floor of Adora’s bedroom. The investigation in Wind Gap is reopened, and police find that Amma, along with three of her friends, killed Ann and Natalie. Adora is tried and convicted for the murder of Marian, while Amma is incarcerated in a juvenile detention facility. Camille visits her once, and during their conversation, Amma admits that when Ann bit Adora on the wrist, Amma became indignant about the ways in which she had tacitly agreed to suffer in exchange for Adora’s love. Camille relapses, scarring the unblemished circle of flesh on her back, and moves in with Curry and his wife Eileen, who care for her and “parent” her well for the first time in her life. Camille finds herself worrying often about the night she cared for the sickly Amma—she enjoyed taking care of her younger sister, and wonders whether she has inherited “Adora’s sickness” or whether she is, in spite of the horrors she’s suffered, a kind person after all.