Emma Brody, a violinist for a Celtic rock band in Chicago, has been blind for twenty years as the result of an attack by her abusive mother. She volunteers for an experimental surgery where her doctor, Ryan Pierce, equips her with corneal transplants. Though Emma's vision is partially restored, a side effect is "retroactive hallucination", meaning some things she sees don’t actually register in her brain until days after first witnessing them.
After hearing a noise from the apartment above and seeing a shadowy figure descend the building stairs, Emma goes to the police to file a report. However, her reliability is questioned because of her impaired vision. When Emma’s upstairs neighbor Valerie is later found murdered, Detective John Hallstrom, who earlier expressed skepticism about Emma, comes to rely on her for clues.
After an appointment with Dr. Pierce, Emma is walking in the parking garage of a hospital when her guide dog Ralphie begins barking and acting jittery. Emma also sees a crucifix pendant left on the garage floor. Ralphie gives chase to an assailant, but is accidentally hit by a car and must be taken to a veterinarian. Hallstrom starts to put more credence in Emma because the crucifix pendant she claims to have seen was found on the earlier victim’s body. He gets a policeman to stand watch at her door and follows her around town, taking a romantic interest in her. When Emma goes on a date with Dr. Pierce, Hallstrom enviously watches from afar.
After Dr. Pierce drops Emma off at her place, Hallstrom follows her back home where they express their mutual attraction to each other, embarking on a romance. Hallstrom’s fellow officers believe his relationship with Emma compromises his detective work. Meanwhile, the serial killer strikes again in Milwaukee. Hallstrom is rebuked by his superior for not having found the killer; to focus on his work, he distances himself from Emma and asks his colleague Ridgeley to look after her.
Emma goes to Hallstrom's office looking for him, prompting an argument between the couple about their relationship and ending with Emma storming off. She gets on the L train and sees visions of a man coming after her, but these turn out to be distorted visions as Ridgeley is the one chasing her, not the killer. Ridgeley finds Emma just as she faints on the train. Later, when seeing Dr. Pierce for an appointment, Emma becomes wary when she sees the doctor using surgical soap, as she remembers this was the scent when she encountered the killer.
Hallstrom finds medical bills addressed to Emma that erroneously lists the upstairs apartment as hers. He pieces together that the murderer meant to kill Emma, but ended up mistakenly killing her neighbor Valerie. He deduces that the killer is going after people who received the organs of Leslie Davison, a woman the killer loved. Dr. Pierce shows up outside Emma’s apartment claiming the family of her organ donor wants to get in touch with her. After some hesitation, Emma gets the address from Pierce and heads to the location with Crowe, her police officer escort.
Emma knocks on the door of the house but nobody is home. She goes to tell Crowe who has parked in an empty garage, but she is ambushed by the killer, who has killed the cop in his car and locked the garage. The murderer, a former hospital orderly, refers to Emma as Leslie and taunts her. Emma fights back, gets ahold of his gun and shoots, but her impaired vision makes it difficult. When Hallstrom is informed that Emma went to Leslie’s supposed address, he goes to the location with backup. After a prolonged chase around the garage, Emma manages to shoot the killer dead. The cops hear the gunshots and bring Emma to safety.
After some questioning at the police station, Ridgeley offers to give Emma a ride home, but Hallstrom is waiting outside with a recovering Ralphie. Emma decides to walk home with Hallstrom and they share a kiss.
