Charles Schine (CLIVE OWEN) is a commercial executive whose marriage to wife Deanne (MELISSA GEORGE) might be strained, but their love for their diabetic daughter Amy (ADDISON TIMLIN) -- whose medical needs has financially tapped them -- isn't in question.
One day, while on the way to work via the commuter train, Charles realizes he doesn't have enough money to pay for his ticket. Just then, a stranger, financial worker Lucinda Harris (JENNIFER ANISTON), offers to pay his way. The two end up becoming commuting friends, eventually leading to lunches and then the thoughts of having a fling despite her saying she's also married, albeit unhappily, with a child. After a night of drinking and some hesitation on both their parts, they get a room.
And then the door bursts open and Laroche (VINCENT CASSEL), a French thug storms in to rob them, but ends up beating up Charles and sexually assaulting Lucinda. Stating that her husband would take their daughter if he learned she was cheating on him, Lucinda tells Charles they can't call the police. Thus, he lies to both his family and coworkers, such as mail room guy Winston Boyko (THE RZA), about being mugged.
He thinks the incident is behind him, but then Laroche -- who has his and Lucinda's wallets -- calls him up, demanding money since Charles canceled his credit cards. Charles complies, meeting Laroche's violent accomplice Dexter (XZIBIT) in the process, but then realizes he's never going to get rid of Laroche who's embedded himself deeper into Charles' life and family, with Deanne and Amy unaware of who or what he really is, and with Charles unable to tell them lest his adulterous ways be revealed.
Charles then decides to bring in outside help, but when that person is killed, he must not only deal with a local cop, Detective Church (GIANCARLO ESPOSITO), thinking he's the prime suspect, but also Laroche who's becoming increasingly demanding and dangerous to him and his family.