Piano composer Dong-sik (Eun-shim Lee) and his pregnant wife (Jeung-nyeo Ju) need extra help around the house, so they hire a housemaid (Kim Jin-kyu), whose precociousness soon gives way to troubling behavior. Tensions between her and Dong-sik lead to an affair, and while the pregnancy ends in a miscarriage, it also results in the maid becoming obsessed with killing the entire family, starting with their older son. Soon their comfortable home becomes a physical and psychological battleground.