The film opens on a crowded city street where tragedy interrupts the day: a young woman jumps to her death from a building ledge. Eun-yi, who works in a bustling restaurant, is drawn to the scene and persuades her coworker and roommate to drive her there, lingering over the chalk outline that marks where the woman’s body lay. The next morning, an older woman named Byeong-sik (also known as Miss Cho) visits her small apartment and quietly expresses interest in offering a job. The encounter marks the beginning of a fraught sequence of power, desire, and social divide that will pull Eun-yi into a family life she did not anticipate.
Eun-yi is hired as an au pair for Hae-ra, who is pregnant with twins, and her very wealthy husband Hoon. Her primary duty is to care for the couple’s young daughter, Nami, a task that allows Eun-yi to form a gentle bond with the child. As she settles into the rhythm of the household, Hoon begins to flirt with Eun-yi, offering glasses of wine and playing the piano as a lure, and the two eventually slip into a sexual relationship. Despite the affair, Eun-yi remains outwardly warm toward Hae-ra, the oblivious wife, even expressing genuine delight at the progress of Hae-ra’s pregnancy and the life growing inside her.
Meanwhile, the other live-in maid, Byeong-sik (Miss Cho), witnesses the affair. She tries to pry details from Eun-yi, but Eun-yi keeps her distance. Later, Miss Cho shares her suspicions with Hae-ra’s mother, Mi-hee, who visits the home and orchestrates a chilling “accident.” A ladder at the top of the stairs becomes the stage for a fall; Eun-yi clings to a chandelier as she pleads to be pulled over the railing, but Mi-hee does not help. The fall leaves Eun-yi with a concussion, and she spends the night in the hospital. In a bitter twist of fate, Eun-yi discovers she is pregnant and begins to weigh whether abortion might be the safer option.
The affair becomes public within the family’s circle, and Mi-hee instructs Hae-ra to ignore it, arguing that all wealthy husbands cheat and that a life of quiet luxury is worth preserving. That night, Hae-ra confronts Eun-yi with a golf club but cannot bring herself to strike. The next day, Hae-ra and her mother forcefully confront Eun-yi, offering a large sum—$100,000—to get an abortion and leave. Knowing Eun-yi would not terminate her pregnancy for money, Hae-ra instead takes matters into her own hands by poisoning the herbal medicines Eun-yi takes daily. The next chapter follows as Hae-ra goes to the hospital and gives birth to her twin sons, while Hoon visits, and Hae-ra’s ill will toward him is made clear.
Furious, Hoon returns home to find Eun-yi in his bathtub, where she reveals that she is pregnant with his child and plans to keep the baby. Eun-yi then collapses from the lingering effects of the poisoning, and Mi-hee arranges an abortion without Eun-yi’s consent. After the procedure, Miss Cho reveals to Eun-yi that she was the one who told Mi-hee about the pregnancy. Although angry, Eun-yi forgives Miss Cho and vows to seek revenge on the family. As she recovers, Eun-yi quietly plans her return to the house, aided by Miss Cho, and secretly enters again.
Hoon eventually discovers Eun-yi breastfeeding one of the newborns. Hae-ra orders Miss Cho to expel her, but Miss Cho refuses and quits on the spot. In a climactic turn of events, Eun-yi confronts the entire family—Hae-ra, Mi-hee, Hoon, and Nami—and, in a harrowing moment, hangs herself from the chandelier and sets her body ablaze, leaving the family to watch in horror.
The final scene shifts to a stark, snowy outdoors where the family gathers to celebrate Nami’s birthday, all speaking English as if to sever ties with the world they know. Hae-ra sings “Happy Birthday,” and Hoon hands a glass of champagne to Nami, a moment that underscores a sense of detachment and unspoken insanity that lingers over the family as the camera lingers on Nami’s gaze.
