In 1984, young Deborah Tennis Natasha Lyonne is electrocuted by a microphone during a stage performance at the Victoria Theatre in San Francisco, which her family owns and operates, but she miraculously survives. Sixteen years later, the introverted Deborah works as a librarian while running the theater’s run‑down operation, a venue that mainly screens revival titles of exploitation and horror. With her father gone, Deborah endures the controlling presence of her abusive mother, Tammy [Julie Caitlin Brown]. When Tammy confronts Deborah about selling the theater, Deborah erupts in a brutal rage and stabs Tammy to death in the lobby just as a screening is about to begin.
In a panic, Deborah rushes to the projection booth to start the film, but she accidentally screens security footage of the murder she just committed. The patrons — including Steven Thompson Thomas Dekker, a teenage film buff — mistake the footage for a short film and applaud it as if it were art. Mr. Twigs [Jack Donner], a longtime projectionist who despised Tammy, helps Deborah hide Tammy’s corpse in the theater attic. The unhinged Deborah then commits a second murder with Mr. Twigs, this time of a theatergoer named Veronica [Kat Turner], and films the act; in the footage, Deborah plays a Victorian queen while she and Mr. Twigs cut off Veronica’s breasts with a guillotine. They screen the footage as a short film before another main feature, shocking the audience and drawing a growing cult following to the theater.
Steven’s mother Linda [Cassandra Peterson] begins to worry about her son’s fascination with Deborah’s brutal material, even as Steven becomes increasingly enamored with Deborah, heralding her as a pioneering female horror director. To generate new material, Deborah and Mr. Twigs pose as family members of Veda [Jade Ramsey] and Vera [Nikita Ramsey], two sociopathic twin sisters who are about to be released from a child psychiatric hospital for murdering their parents years earlier, and they manage to take the girls under their wing. Deborah also encounters a violent vagrant, Adrian [Noah Segan], and recruits him to assist in making new films.
Under Deborah’s direction, the group ambushes Evelyn [Mink Stole], Deborah’s librarian coworker, as she is closing up the library, filming as Deborah stitches Evelyn’s mouth shut and locks her alive in the theater attic. Evelyn’s torture footage, titled The Maiming of the Shrew, is shown at a subsequent screening, attended by Steven, who is accompanied by his popular classmate Claire Cavanaugh [Lyndsy Kail]. During the show, Deborah stabs Claire to death in the bathroom and films it with the help of Veda and Vera. Meanwhile, Evelyn tears open the sutures in her lips and screams for help from the attic, only to be beheaded by Mr. Twigs. Steven discovers Claire is missing, but the police dismiss his claims when Deborah accuses him of being an obsessed fan.
Steven’s friend Judy [Ariel Hart] visits the theater to interview Deborah for their school newspaper, but she is bound and gagged and locked in the attic when things go wrong. Steven suspects Deborah’s influence, but Deborah taunts him by announcing that she is shooting her debut feature film and has "just started casting." Steven attends Deborah’s premiere with his mother Linda and Judy, while Veda and Vera prepare punches laced with cyanide to poison the audience as part of a planned toast filmed by Mr. Twigs.
Steven’s bold move to warn others disrupts the deadly plan, and chaos erupts as guests realize they are trapped inside. Adrian is killed when Evelyn’s corpse falls on him from the attic, and Lolita [Ashley Fink], a popular classmate, stabs Mr. Twigs to death as Veda and Vera attempt to start a fire to incinerate everyone inside; the guests nonetheless manage to escape. Deborah kidnaps Linda on the theater’s roof, where Steven confronts her. Deborah outlines her plan to kill Linda as the finale of her movie, claiming that “the audience roots for the killer,” but Steven’s rebuke shatters her resolve, and Linda wrests the knife from Deborah and stabs her in the throat, sending Deborah tumbling to her death.
Outside, the escaped twins Veda and Vera stagger out, each brandishing a knife and ultimately stabbing each other to death. After the smoke settles, the news wonders whether Deborah’s work might ever become a film in itself, but Steven doubts such a thing would ever truly happen, remarking that if it did, Deborah might rise from the dead by now. He then leaves the scene with his mother and Judy, passing Deborah’s corpse as they walk away. The Victoria Theatre remains a place of dark legend, where a killer’s “finale” becomes a disturbing myth in the eyes of those who survived.
