Teenager Maggie Thompson relocates to her hometown in Ohio with her mother, Erica, after her father leaves them. As Maggie starts her new life at school, she quickly bonds with her peers Haley, Darrell, Chaz, and Andy—who becomes infatuated with her. In an attempt to have some fun, they persuade Sue Ann "Ma" Ellington, who works as a veterinary technician, to procure alcohol for them since they are underage. However, Sue Ann later tips off the authorities about their activities. Luckily, they are let go due to the officer's previous dealings with Andy’s father, Ben.
The next day, Sue Ann invites the group to her house, where she has transformed her basement into an inviting party space complete with decorations. Before long, she's the center of attention among the students, relishing her newfound popularity. Yet, her overbearing nature soon starts to wear on them, as she increasingly pushes them to include her in their activities. One evening, witnessing a romantic moment between Maggie and Andy stirs up jealousy in Sue Ann, leading to a shocking turn of events. Consumed by her feelings, she drugs Maggie and takes her earrings.
Upon awakening, Maggie is horrified to find herself disoriented, with her precious earrings missing and her body bearing bruises. Distraught and frightened, she confides in Andy, assuring him that she no longer wishes to visit Sue Ann’s home, and he agrees to stay away as well. In a twisted bid for regaining their trust, Sue Ann fabricates a story about having pancreatic cancer to explain her strange behavior. However, Haley soon spots a bracelet on Sue Ann that belongs to one of their friends, sparking suspicion of theft among the girls.
Determined to uncover the truth, Maggie and her friends decide to investigate Sue Ann's house. Upon arrival, they are met by Genie, Sue Ann's daughter from a previous marriage. To their surprise, Genie appears fully able-bodied rather than the wheelchair-bound person they had been led to believe she was. She warns the kids just as Sue Ann comes home, resulting in their narrow escape.
Meanwhile, Ben makes a trip to Sue Ann's workplace to drop off his cat and unexpectedly invites her out for drinks. During this encounter, Sue Ann is confronted by Ben about his son's frequent visits. He warns her to keep her distance from Andy, calling her “pathetic.” Flashbacks reveal the humiliating encounter that scarred Sue Ann in high school when Ben tricked her into a compromising situation that led to public ridicule, a trauma that has haunted her ever since.
As Sue Ann spirals deeper into madness, she commits horrific acts, such as running over Mercedes with her truck and even killing her boss. Her actions take a darker turn when she draws blood from Maggie’s dog, Louie, and lures Ben to her home, where she knocks him unconscious. When Ben awakens, he finds himself trapped, and Sue Ann prepares to inflict a brutal fate upon him.
Maggie ultimately shares the frightening truth about Sue Ann with her mother, only to find herself grounded. In retaliation, Sue Ann sends Maggie a photo of herself with Andy at a party, intensifying Maggie’s heartbreak. Outraged that Andy returned to Sue Ann's house, she sneaks out to confront him, only to discover that their friends have been drugged and that Ben’s lifeless body is hidden within the horror of what has transpired.
Chained in Sue Ann's basement, the friends become victims of her violent delusions as she performs disturbing acts upon them, revealing a sinister belief that only she deserves a place within their social circle. As tensions escalate, Sue Ann grows wary of Andy, who tries to manipulate her emotions, leading to a tragic confrontation.
When the inevitable rescue attempt arrives, chaos erupts as Sue Ann’s house is engulfed in flames. In a desperate fight for survival, Maggie saves Genie, while the others awaken to the horror of what has occurred. As the fire rages on, Maggie, Erica, and Stu, a co-worker, work swiftly to rescue the trapped friends. Meanwhile, Sue Ann's final whims take her to bed with Ben’s corpse as the flames consume her twisted fantasies.
