In the opening shot, a news report is broadcast on the criminal Colin Evans (Idris Elba). He is up for parole after serving five years on a manslaughter charge after killing a man and also taking the lives of five women. Colin gives his testimony to the parole board, claiming he was ashamed of his actions and that he is ready to return to society. However, the chairman of the board doesn't buy it for a second, claiming Colin is a malignant narcissist and a violent offender, and everyone there knows that the families of the five women would not be happy to see him walking free. The words of the chairman echo in Colin's head, and his parole is denied.Colin is being taken back to prison in a van when he appears to have a bloody nose. He asks for help, only to grab the guards gun and put him in a headlock. The driver stops and aims his gun at Colin. Colin calmly tells the driver to put the gun down, and he does. Then he shoots both the guard and the driver, free to make his escape.We meet Terri Granger (Taraji P. Henson), holding her baby Sam and trying to talk on the phone, while landscapers are working outside her house and her daughter Ryan (Mirage Moonschein) rides around the house. Terri's best friend Meg (Leslie Bibb) comes jogging in. She notices how overworked Terri is, so she suggests having a girls night. Later, Terri's husband Jeffrey (Henry Simmons) comes home, only to get packed for a trip for his father's birthday. He seems unhelpful and impatient with Terri, though he assures her he loves her.Colin is now in Atlanta, Georgia driving a van, stalking a woman named Alexis (Kate Del Castillo). He sees her meeting a man outside a cafe, and Alexis hugs him. He breaks into Alexis's home before she gets back, and he confronts her over her not waiting for him once he got out. He takes out a note that says "Didn't want to wake you up because you look so beautiful when you sleep." Scared, Alexis runs for the door, but Colin blocks her. She runs to her room where Colin makes her admit that she was sleeping with another man. Again, the words ring through his head, and he puts his hand on Alexis's throat. He breaks her neck and then brutally beats her with a lamp.At night, a heavy storm starts brewing. Terri gets her kids ready for dinner. Colin drives his van into a tree after swerving off the road. He walks until he gets to Terri's home. He rings the bell, and she answers. Colin asks to use the phone to call for a tow truck. After supposedly using the phone, Colin tells Terri that the tow truck will come later. Terri invites him inside and mends a cut on his forehead. Colin is charming and polite toward Terri, as well as Ryan when she comes around. Terri serves Colin tea and asks him if he is seeing anyone. He says he had an ex-fiancee that he caught cheating on him.Meg comes over with wine and is attracted to Colin. They share the wine and Meg makes comments about how Terri used to be a wild girl and asks Colin if that's a surprise. He says not at all. While Terri goes to check on her kids, Colin asks Meg where he can smoke. She directs him to the garage and joins him in the smoke. Meg asks him if there's something going on with him and Terri. He smiles and doesn't say a word, leading Meg to think her friend is having an affair. Colin suggests that Terri is keeping things from Meg, which angers her and prompts her to confront Terri, until Colin takes a shovel and kills Meg with it. He drags her body to the side.Terri sees Colin alone and asks where Meg is. He says she left, though Terri notices Meg's umbrella still lying by the coat rack. Terri goes to call Meg and sees the phone lines are cut, and all the knives are missing from their holder in the kitchen. She goes upstairs to see Colin playing with Ryan, and then spots the gun in the back of his pants. Terri orders him to put Ryan down. They leave the room, and Terri reaches for the fire extinguisher and sprays Colin, then hits him over the head so he falls down the stairs. Terri runs to her kids, but Colin quickly manages to get back on his feet and tell her to put Sam down and to go with him. She closes the door to the kids' room, and Colin draws his gun on her, warning her not to do anything like that again. He takes her to the bathroom and makes her stand in the shower with him as he washes himself of the foam. He then makes Terri undress and change her clothes. Thinking he is going to rape her, she tells Colin to get this over with, but he tells her not to flatter herself. Terri grabs a lamp and whacks Colin over the head with it and even manages to stab him in the side. She runs for her kids, but once again, Colin is too fast for her.Colin forces Terri to take her kids to her car so they can make their getaway. While passing through the garage, Terri sees Meg's bloody body lying on the side. On the road, Terri sees a cop and quickly signals him with the headlights when Colin isn't looking. The cop follows them and makes her pull over. Colin grabs Sam and pretends that he was crying and had to comfort him. The cop gets suspicious when Ryan asks for her dad. Terri steps out of the car and tries not to be obvious to the cop as Colin can hear her. The cop notices Terri continuously looking over at the car, and he figures out something is wrong. He tells Terri not to move as Colin steps out of the car, and Colin shoots the cop dead. He rolls the man's body down the hill.Colin makes Terri drive to Alexis's home. He brings her up to the room where her body is still lying. He ties Terri up but is pulled away when her car alarm goes off. Alexis's cell phone starts ringing. Terri manages to cut herself loose and answer the phone. A man's voice answers saying he's been calling multiple times, but Terri recognizes the voice belonging to Jeffrey. However, he replies, "Alexis?" Thus, Terri puts it together - Colin got Jeffrey's name and address off the note that he found near Alexis's bed earlier that day, and it was no accident that he came across her home. He's been seeking revenge. Terri then tells Jeffrey that Alexis is dead and to call the police. She runs to get the kids, but Colin is walking back to the house. Terri hides the kids in the closet and runs upstairs, grabbing a knife for protection. Colin nearly finds the kids, but Terri distracts him. He catches her in the bedroom and starts to fight Terri. He tries to strangle her, but she jabs him in his side wound with her keys, and even beats him with something heavy. He appears unconscious until he grabs Terri and takes her down. Then she grabs Colin's gun and shoots him once, then again, and then multiple times until he falls out the window to his death.The police arrive, along with Jeffrey. He finds Terri and tries apologizing to her, but she responds by punching him hard in the face.A while later, Terri has moved to a new home with the kids. She still carries a picture of her and Meg. She now has a new friend that helps her take care of the kids, and they take them to the park during a sunny afternoon.