Police officer Harry Siegal is interrogating Rory, who has kidnapped a senator's son, Matthew. Harry beats Rory mercilessly until he finally tells where the boy is, locked away upstairs. Harry runs upstairs and breaks in to free the boy. In the aftermath, the medics take the boy away while the other officers praise Harry. Harry's superior warns that Internal Affairs will be all over him. Rory is in critical condition but with his dying breath he says that Harry won't forget what happened.
Later, Harry meets with the Internal Affairs detective, who notes that Harry has tortured dozens of suspects in the past but despite that has never shot anyone. The investigator informs Harry that he'll only have to serve a hundred hours of community service… but he's going to lose his badge and his pension.
Fifteen Years Later
Now using the name Harry Bender, Harry is working as a private detective with partner James, working divorce cases. He gets the evidence against a cheating husband, Richard, and takes it to his wife. However, Harry then blackmails her with the tapes he made of her having an affair. Afterward, Harry notices James carrying a gun and tells his partner he never wants to see the gun again. Once James is gone, Harry gets a call from a prospective client, social worker Meredith Kane. He meets with her the next morning at a diner and she asks him to investigate whether her husband Jack is having an affair in their home when she isn't there. She asks Harry to run the surveillance from a vacant house across the street so Jack won't spot their van. Harry agrees and checks out the house during the day. As he leaves, he's unaware that someone is watching him from inside.
Later, Harry and James set up their equipment in the house. Harry looks around and sees graffiti of four white-faced figures dressed in black, standing around a pentagram. That night, Harry watches from the house while James is in the van down the street. Jack hasn't shown up but Harry hears some static over his shotgun mike and sees a light on the second floor. James doesn't see it but Harry hears voices of people talking about beatings and torture. The light goes out and the sound goes dead, and Harry starts drinking. The voices suddenly come back and Harry figures they're coming from within the house he's at. He checks out the place and finally finds a neighborhood kid who took a dare to stay the night. The boy mentions that the house killed four kids years ago. Harry kicks him out and goes back to his post, unaware of a radio starting up on its own behind him.
Back on station, Harry hears a man and woman on the second floor and sees a light go on. However, the woman says that Siegal burned her with cigarettes and Harry recoils in terror. Looking down, Harry sees blood on the floor. He goes into the next room where sees the four graffiti figures... and one's throat is cut as he looks on.
The next day, Harry meets with Meredith and tells her he's calling off the investigation. She insists that Harry continue with the case and offers to listen to him if there's something wrong. Harry admits he's done some bad things and they're starting to come back. Meredith says she had a brother that made some big mistakes, but everyone has done bad things and people can try to make up for them in the future.
Harry returns to the case with James and has his partner go over the video he took the previous night, then goes into the vacant house. As Harry watches Meredith's house, James says there's nothing on the tape and wonder's if Harry dreamed the entire thing. Harry suddenly hears the TV come on and sees two children watching a 1950s program in the living room. He also sees a light in the upstairs window and a figure with a knife. Behind him, one of the graffiti figure's necks has a cut appear on it. Harry runs over to the house and breaks in, only to find that the place is empty except for a table with "For Sale" brochures. As he goes outside, he sees a man at the window where he was running surveillance from.
Harry storms into the house and demands to know who is missing with him. He switches to night-vision goggles and spots a man in front of him, who runs away leaving a blood trail. Harry finally catches up to the man: Rory. Rory asks "Why are you so bad?" A light flares up and Harry rips off his goggles, to find a light shining through a door. He goes inside and finds himself in a suburban home in the 1950s, with a carton of milking spilling onto the table. The carton has a picture of a missing boy on it. Harry runs in terror back through the door and to the present, where he sees a man driving nails into his mouth. The man calls out Harry's name and Harry runs away in terror and tries to get out. Rory appears and asks him again "Why are you so bad?" Harry insists he never hurt anyone who didn't deserve it, but Rory says that the girl Harry burned was innocent. Harry backs up, and finds himself in the 1950s. Two boys are watching the TV and the older one shows the other their dad's gun. The older one talks about how he wants to be a cop like their father and dares his younger brother to hold the gun. The younger one takes it and they start to play… and he accidentally shoots and kills his brother. The father shows up and talks to the younger boy: Harry. The father makes him swear that they'll never reveal what happened to the older brother, Max.
The next morning, Harry looks at the graffiti figures while Rory says that the house made them understand and they're at peace. He asks if Harry wants to be at peace as a painting of Harry cutting his throat appears on the wall. Harry holds the knife to his throat and starts to kill himself… and realizes one figure is missing. He remembers that Meredith was wearing a scarf to cover a scar on her throat, and that she wants this to happen.
Harry runs out to the van where James is dozing and drives away while tracking Meredith's billing address. They drive to her apartment and Harry tells James to call the police if he's not back in ten minutes. Inside, Meredith is looking at a gun and saying that if she'll have to, she will. She puts the gun back in a drawer and then calls Harry. Harry bursts in and demands to know why she set him up. She says that Rory told her to do it: Rory was her brother. "They" promised that she could see Rory again, so she and the other kids went in and the house showed each kid something they couldn't live with. Rory protected her so that she could make Harry suffer. She says that Harry's dead inside, and he remembers back to when as a young boy he and his father buried Max.
While Harry says it wasn't his fault, behind him Meredith takes out her gun and prepares to shoot him. He disarms her and she yells at him to shoot her, but he refuses and says he's going to change things from now on. However, James comes in with his gun, sees Harry with the gun, and Meredith yells for help. James shoots Harry then apologizes to the dead man, while Meredith laughs in triumph.