Chicago advertising executive Charles Schine lives with his wife Deanna and their daughter Amy, who suffers from type 1 diabetes, which requires expensive medication.
On a commuter train to work one morning, Charles meets Lucinda Harris, a financial advisor who is also married with a daughter. A mutual attraction develops and the two begin meeting frequently. They soon decide to consummate their affair in a run-down hotel. As Lucinda is unzipping Charles' pants, they are interrupted by an armed man who beats Charles and brutally rapes Lucinda. Not wanting their spouses to learn of their affair, Charles and Lucinda agree not to report the crime and then go their separate ways.
Days later, the man, who identifies himself as Philippe LaRoche, contacts Charles and threatens to kill his family if he does not pay him $20,000. A month later, LaRoche calls again, this time demanding $100,000. Charles explains his situation to his work colleague Winston, an ex-con who works as a repairman in his building. Winston offers to scare off LaRoche for ten percentage of the payout. Charles embezzles $10,000 from his company and he and Winston plot to get the drop on LaRoche at his specified meeting location. However, LaRoche surprises him, shoots Winston dead and takes the money. Charles disposes of Winston's body and gives a false alibi when questioned by Detective Franklin Church.
Charles later receives a call from LaRoche; he is holding Lucinda hostage and will kill her if he does not deliver the $100,000. Charles takes the money from an account meant for his daughter's medical treatment and makes the payoff to LaRoche and his partner Dexter. Charles then visits Lucinda at work and discovers she is actually called Jane, who worked there briefly as a temp. He goes to Jane's apartment, which is being shown to prospective renters, and finds that Jane's photograph of her supposed daughter is actually a cut-out of a stock picture from a brochure.
Charles tracks Jane down and sees her kissing LaRoche, learning she was in on the scam. He also observes her seducing another unsuspecting businessman, Sam. Charles rents a room at the same hotel as before and waits for Jane to go there with Sam. Determined to retrieve his stolen money, Charles knocks LaRoche unconscious outside the hotel room door, disarms him, and reveals to Sam the scheme he has been set up for. Dexter arrives to back up LaRoche and a gunfight ensues; nearly everyone is fatally shot but Charles, who returns to his room and convinces the police he was just a bystander. Before leaving, Charles claims his briefcase and gets back the money.
Later, Charles is suspended from work for the embezzlement and is sentenced to six months of community service, teaching in a prison. During one of his classes, he comes across a notebook containing a story about him written by one of the students. Charles finds LaRoche, who had survived the gunfight. LaRoche threatens to continue to disrupt Charles' life but Charles reveals that he has planned their encounter and then stabs LaRoche to death with a shank.
Charles walks away from the encounter by claiming to Detective Church that LaRoche attacked him and he reacted in self-defence. He returns to his family.
Clive Owen as Charles Schine
Jennifer Aniston as Jane ("Lucinda Harris")
Vincent Cassel as Philippe LaRoche
Melissa George as Deanna Schine
Giancarlo Esposito as Detective Franklin Church
RZA as Winston Boyko
Xzibit as Dexter
Addison Timlin as Amy Schine
Tom Conti as Eliot Firth
Rachael Blake as Susan Davis
Denis O'Hare as Jerry the Lawyer
Georgina Chapman as Candy
David Morrissey as Sam Griffin
David Oyelowo as Patrol Officer
Danny McCarthy as Correctional Officer Hank
Ortis Deley as Cop
Richard Leaf as Night Clerk Ray
Catherine McCord as Avery Price Receptionist
based on the novel of the same name by James Siegel.