The film centers on Ann, Barbara Steele an introverted, solitary woman who keeps to herself in a dim apartment building, sharing the space with her neighbor Claudia and Claudia’s daughter Julie. Ann micromanages a private butterfly world inside her home, a room she treats as a sanctuary where every specimen is pinned with quiet reverence. The story opens with a tense moment when a workman balances on a ladder to trim a tree; Ann abruptly knocks the ladder away, sparking a chaotic sequence that draws in Nick, the workman’s boss, Ray Wise who rushes out to apologize, unaware of Ann’s control over what happens around her.
Julie, who has been locked out by her unreliable mother, is invited inside by Ann to pass the time until Claudia returns. When Claudia arrives, she invites Ann to dinner as a thank-you for watching over Julie. The dinner scene is layered with tension, but the most unsettling moment comes when the workman arrives at Ann’s place to repair damage from the ladder incident. He mentions that he once saw Ann scolding a young girl in the corridor, which makes Ann deny noticing him. Subsequently, in a moment that shifts the tone from domestic to dangerous, Ann lures the workman into the butterfly room and sprays him with acid bought from a nearby taxidermy shop.
The film then flashes back to earlier scenes that reveal the roots of Ann’s obsession. It first shows a confrontation where she scolds a young girl, followed by a mall encounter with a lonely girl named Alice, played by Julia Putnam. Alice explains that money given for a doll was stolen, and Ann buys her a new doll. Alice asks for Ann’s address and promises to repay her later, but she later discards the doll in a trashcan. In a later visit, Alice returns a portrait she has drawn for Ann, who in turn gifts a blue butterfly pin. Alice notices a handmade ornament with Dorothy’s name on it and learns that Dorothy is the deceased daughter Ann speaks of. As the flashbacks unfold, a second thread shows that Alice visits Ann again, and the two form a cautious, complicated connection.
In the present, Ann enters a rundown apartment block and retrieves a blue-framed butterfly, a symbol of her control over the space that also contains a hidden life. She manipulates the elevator by stopping it and revealing a trap door beneath; when someone calls the lift again, she panics and covers the trapdoor with a rug, concealing a body. Later, Claudia and Julie share a meal, and Claudia reveals she is pregnant, while Dorothy—Ann’s estranged daughter and a protective force in Julie’s life—warns against Ann’s influence. The tension escalates as Nick fixates on the fragile wall that separates the butterfly room from the rest of Ann’s apartment and proposes illegal demolition for money, moving a dresser to shield the protected space.
Ann’s violent impulses intensify when she discovers Alice accompanied by Olga, a woman connected to Olga’s life in the mall flashbacks. Following them into the bathroom, Ann kills Olga, an act that reveals the depth of her capacity for harm. Dorothy confronts Ann outside her apartment, asserting that she will not let Ann harm Julie and underscoring their fractured history; the revelation that Dorothy is the daughter Ann abandoned casts the conflict in a new, personal light. Claudia’s pregnancy and abortion plans further strain the fragile web of relationships, with Dorothy warning Claudia about Ann’s true nature. When Claudia later confronts Ann in the butterfly room, Ann’s violence erupts again, and she kills Claudia.
Julie’s world grows increasingly perilous as she uncovers disturbing discoveries: a disfigured man's corpse in the butterfly room and Alice’s corpse, both found by Julie herself. In a desperate moment, Julie redials Dorothy, who answers the call and becomes a crucial anchor in the escalating danger. Dorothy ultimately confronts Ann with the necessity of protecting Julie, and a dramatic chase ensues that ends with Dorothy running Ann down with her car on the street.
The film closes on a chilling note of bittersweet defiance. Julie survives and celebrates her birthday, having been adopted by Dorothy, who appears calm yet haunted by the revelation of Ann’s cruelties. The final shot lingers on Dorothy as she stares into the camera, a quiet acknowledgment of the enduring consequences of Ann’s fixation and the fragile line between protection and danger that marks Julie’s world.
