Vanessa Lutz (Witherspoon) is a poor, illiterate teenage girl living south of Los Angeles. Her mother, Ramona (Amanda Plummer), is arrested in a prostitution sting and her stepfather, Larry (Michael T. Weiss), is taken into custody on drug and child abuse charges. Social worker Mrs. Sheets (Conchata Ferrell) comes to take Vanessa away, but Vanessa handcuffs her ankle to a bed and runs away. She takes her parents' run-down car and plans to go to her grandmother in Stockton. Along the way, Vanessa stops to see her boyfriend and classmate Chopper Wood (Bokeem Woodbine), a local gang member, to tell him about her excursion and he gives her a gun to sell upon arriving at her destination. Minutes after Vanessa leaves, Chopper is killed in a drive-by shooting by rival gang members. A little later, Bob Wolverton (Sutherland), a counselor at a school for boys with emotional trouble, picks her up after her car breaks down and offers to take her as far as Los Angeles where he is headed.
Over the long drive, Vanessa comes to trust Bob, and confesses to him the details of her painfully dysfunctional life, including being sexually abused by her stepfather. At one point, Vanessa shows Bob a photo she keeps in her wallet of her biological father. That evening, Bob reveals his true nature: he is a serial killer of young girls known in the press as the "I-5 Killer". He tries to kill Vanessa when she refuses to give in to him. The tables are turned, however, as Vanessa eventually pulls out her gun and shoots him several times before escaping. She goes to a local restaurant where her blood-stained appearance attracts attention from the patrons and staff.
After leaving the restaurant, Vanessa is quickly arrested and questioned by two police detectives, Mike Breer and Garnet Wallace, who write her off as a carjacker, even though she insists Bob had tried to kill her and had told her about his other murders.
Bob has survived, but the bullet wounds have left him severely handicapped and disfigured. Vanessa is put on trial, with everyone believing that Bob is the innocent victim he claims to be since he has no criminal record, while Vanessa has a long record and is a veteran of juvenile homes. Vanessa goes to prison, while Bob and his socialite wife Mimi (Shields), who knows nothing of his crimes, are treated like heroes.
Scared at first, Vanessa eventually makes friends in prison, including a heroin-addicted lesbian named Rhonda (Brittany Murphy) and a brutal Hispanic gang leader named Mesquita (Alanna Ubach). Undaunted, Vanessa plots to escape and continue her journey to visit her grandmother. Remembering what her stepfather taught her about life in prison, Vanessa constructs a crude knife from a toothbrush as a weapon. The following evening, Vanessa and Mesquita are being transferred to a new maximum security prison. En route, Mesquita and Vanessa subdue and escape from the prison guards assigned to escort them, with Mesquita killing one. After their escape, Vanessa and Mesquita part ways as Mesquita goes off to be reunited with her gang, and Vanessa continues her journey to her grandmother's house.
Meanwhile, detectives Breer and Wallace re-examine evidence found at the scene of Bob's shooting and begin to suspect that Vanessa was telling the truth. They then search Bob's home, where they find violent child pornography in the locked shed adjacent to the house. Confronted at last with what her husband really is, Bob's wife commits suicide. Arriving home at just that moment to find police cars outside his house, Bob panics and flees to Vanessa's grandmother's house. He finds the address to the grandmother's trailer park written on the back of a photograph Vanessa had on her.
While posing as a prostitute, Vanessa steals a car from a prospective john and drives to her grandmother's house. Vanessa finds Bob lying in wait with a gun. Paralleling the big bad wolf in the classic children's tale, Little Red Riding Hood, he is in the grandmother's bed wearing her nightgown and nightcap with the covers pulled up to his nose. The animated opening credits of the movie actually foreshadow this climax with the big bad wolf assiduously pursuing Little Red Riding Hood. Vanessa is even seen carrying a basket in the movie. Bob reveals himself and then Vanessa sees her grandmother's dead body on the floor. A fierce struggle ensues culminating in Vanessa strangling Bob. Detectives Breer and Wallace arrive and approach the trailer cautiously with their guns drawn when they hear the commotion inside. Vanessa eventually exits the trailer exhausted after her struggle and the detectives enter to find Bob and Vanessa's grandmother both dead. Outside, Vanessa sits in a chair drained, near her breaking point, when she looks up to ask the detectives if they have a cigarette. They smile and Vanessa responds in kind.
Who is lying in wait for Vanessa at her grandmothers?
Bob