Plot
Following a brutal attack in a parking lot, violinist Ellen Ashland wakes up in hospital to learn that she has been blinded. During her recuperation at the hospital she receives a phone call from her brother, who says he has found an apartment for her. Ellen wakes in her new apartment with no memory of having travelled there. Clayton arrives, a nurse her brother has hired to care for her as she begins to adjust to life without sight.
From one of her windows Ellen can feel a breeze and hear traffic below. But she can’t hear any sounds from the other window in her living room. When she questions Clayton, he says the window just has thicker glass.
One night, Ellen hears the voice of a woman in distress; she initially believes the woman is in her apartment, but then realises the noise is coming through the vent from the adjoining apartment. The following morning, she goes next door and puts up a sticky note on her neighbour's door asking her to join her for tea.
Later that day, her neighbour shows up and introduces herself as Lana. Ellen is suspicious of Lana as she seems scared to talk. Lana tries to leave Ellen's apartment but when Ellen tries to stop her she touches Lana's face, and is alarmed to feel a wound with stitches. Lana reacts by whispering "trust no one" and then flees Ellen's apartment upon the arrival of her abusive husband, Russo.
Ellen contacts Detective Bryce (the officer working on her assault case) who sends Officer Neiman to check on Lana; he confirms she is okay and does not have any recent wounds. Ellen expresses her concerns to Clayton but he tells her that he has met Lana, that she seems unhinged, and Ellen should not worry about her.
Later that day Ellen is standing near her door when she hears footsteps. At first she thinks it's Lana and begins to apologise to her for the misunderstanding, but it’s Russo, who warns her to stay away from his wife, and says he will be talking to the building management about her.
A few moments later Clayton arrives and a frantic Ellen tells him that Russo has threatened her. Angry and protective, Clayton says he will talk to Russo, but Ellen stops him. Then Clayton hints that he has feelings for her, but when he confesses this, Ellen turns him down and he leaves dejected.
Hearing someone enter the apartment, Ellen thinks that Clayton has returned and begins to apologise. However the newcomer attacks Ellen. Hearing the assailant’s breathing pattern she recognises it as that of the person who attacked her in the parking lot. She manages to dial 911 before passing out. She is awoken by a paramedic and a worried Clayton, who informs her that Detective Bryce is here to see her. Detective Bryce reassures her that after Clayton left her apartment, nobody else entered. Detective Bryce also confirms to Ellen that her friend Sasha, who was having an affair with Ellen's ex-husband, is the prime suspect in Ellen's attack. Feeling alone and unsure of anyone, Ellen is overwhelmed and decides to commit suicide. She writes letters to her brother, Sasha, and Clayton, and then jumps from her apartment balcony.
Ellen wakes up on the floor of a soundproof room and quickly realises the apartment she was staying in was fake, and all of the noises "outside" were coming from a speaker system. She explores the hallway only to find she cannot escape. Ellen finds Lana in the hallway and asks her for help, asking about the place they are living in, and telling her that she knows they are being watched. Lana tells her that this is home and flees before answering anymore questions. Clayton then arrives to cook Ellen dinner and knocks twice; at that moment she realises all of the people she has interacted with since her attack - the doctors, the detective, the paramedic, Russo - were all Clayton playing different roles, but giving himself away by his habit of knocking on any surface twice. Ellen knocks Clayton unconscious and finds Lana who reveals she is Clayton's sister and she helped him kidnap Ellen. She then tells Ellen their only hope of escape is by using the hidden vent in Clayton's room.
Clayton finds and once again captures Ellen. He confesses that after his mother's death, his father kept him captive in the basement for three years. During this time, Lana played recordings of Ellen playing the violin, with the result that he became obsessed with her. Ellen tries to escape via the vent and finds a vial, which she realises is the same substance that was used in the attack that left her blind. She finds her way back to her room, chased by Clayton, and sprays the substance in his face. Upon seeing Clayton disabled, Lana guides Ellen to an exit into the outside world.
Six months later, Ellen prepares to go on stage to the sound of an elated crowd, as an assistant asks her if she needs any help. She declines and walks on stage herself.
