14-year-old Hayley Stark and 32-year-old photographer Jeff Kohlver engage in a sexually charged, flirtatious online chat. They then meet at a coffeehouse before going to Jeff's home. When they arrive, Jeff makes them drinks, but Hayley refuses by saying she was taught to never take a drink she has not mixed herself. Hayley goes to the kitchen and makes them both screwdrivers. As Jeff shows her around his house, she notes the photographs hung on his walls, all of which seem to be of underage half-clothed girls. Hayley asks Jeff to photograph her. He gets out his camera and Hayley begins to pose, but before Jeff can take any photos he loses consciousness.
When Jeff wakes, he is bound to a desk chair. Hayley explains she has been tracking and baiting him through online chats and drugged him because she believes he is a sexual predator and murderer. Jeff denies these allegations, claiming he had innocent intentions. Hayley searches Jeff's house and finds a gun and a safe. In the safe, Hayley finds pictures, including a photo of Donna Mauer, a local girl who has been kidnapped and remains missing. Jeff continues to deny the accusations and kicks Hayley to the ground, temporarily knocking her out. He rolls the chair into his bedroom and manages to retrieve his gun, which Hayley left out on his bed. He returns to the living room to see that Hayley is no longer there; she comes up from behind him and wraps his face in plastic wrap, choking him unconscious.
When Jeff wakes, he finds himself bound to a steel table with a bag of ice on his genitals, making them numb. Hayley tells him that she intends to castrate him. Jeff attempts to dissuade her, including by telling her he was abused as a child in a play for sympathy, but fails. Hayley consults a medical book to guide her through the procedure, describing it to Jeff as she performs the operation. Once it is finished, Hayley puts down the scalpel and puts something appearing to be testicles in the kitchen sink garbage disposal. She turns it on and walks away, saying she needs a shower.
Jeff frees himself, only to realize that the "surgery" was a trick and he is unharmed. He picks up the scalpel and storms into the bathroom, where the shower is running. He slashes at the shower curtain, but finds the shower empty. Hayley attacks him from behind, and as they struggle, Hayley incapacitates him with a stun gun.
Hayley calls Jeff's ex-girlfriend Janelle and, posing as a police officer, asks her to come immediately to Jeff's house. Jeff regains consciousness to find that Hayley has bound his wrists and hoisted him to stand on a chair in his kitchen with a noose around his neck. Hayley makes Jeff an offer: if he commits suicide, she promises to erase the evidence of his crimes, but if he refuses, she will expose his secrets. The conversation is interrupted when a neighbor knocks on the front door, selling Girl Scout Cookies. When Hayley returns, Jeff breaks from his bindings and pursues her to the roof of his house. Hayley has brought her rope from the kitchen and fashioned it into a noose secured to the chimney. Hayley keeps Jeff at bay with his gun.
Jeff confesses that he watched while another man raped and murdered Mauer. Jeff promises Hayley that, if she spares his life, he will tell her the other man's name so she can exact her revenge. Hayley reveals that she already knows his name, Aaron, and that Aaron said Jeff did it before he killed himself. Janelle arrives, and Hayley once again urges Jeff to hang himself, promising that she will destroy the evidence. Defeated, Jeff lets Hayley slide the noose around his neck, and steps off the roof. After he falls, Hayley says, "Or not," then gathers her belongings and walks away through the woods.
