Dr. Juliet Devereau rents an apartment in New York, large and affordable, but with the nearby subway causing noise and vibrations, occasionally even causing objects to fall off the table. She and the owner Max first get along well, and, after being encouraged by her colleague Sydney, she starts having sex with him. However, she does not go through with it because she still has feelings for her former boyfriend Jack, after they split up because he cheated on her.
Max has constructed secret corridors, peepholes, and a one-way mirror, and uses these to observe her in secret. Also, in her absence he secretly enters her apartment to touch her clothes, use her toothbrush, and lie in her bath and masturbate. He also hides under her bed and licks her fingers while she sleeps. He even sedates her, and touches and later rapes her while she is unconscious.
Because his grandfather August, who also lives in the house, criticizes him, Max kills him. Max is also frustrated about the fact that Jack and Juliet reconcile and, observed by Max, have sex in the apartment. Max observes this from one of his peepholes, Since this makes Max jealous, he throws him from a flight of stairs outside, and later, when he visits the apartment, he kills him. Juliet has her blood and urine analyzed, which shows the sedation. Moreover, her security video images show the rape. She confronts Max, who now tries to kill her, chasing her around in the hidden corridors, but she defends herself with Max's nail gun, in passing seeing Jack's body. After failing to make him harmless when she has the chance, Juliet finally kills him.