The story centers on a corporate climber Angela (Nichols) who gets stuck working late on Christmas Eve before leaving to attend a family holiday party. On her way into the parking garage (P2), She gets into the parking garage, only to discover that her car won't start. After receiving some assistance (to no avail) from the security guard named Tom (Bentley) and turning down his offer to spend Christmas with him, she calls for a taxi and waits in the lobby. When the taxi arrives, she discovers she's locked in the lobby, and runs back into the parking garage.The lights soon shut down and Angela wanders only guided by the light on her cell phone,she shines it on herself revealing Thomas right behind her. Thomas assaults Angela, knocking her out.
Later, Angela awakens in a drunken haze inside Thomas's office, her ankle chained to the table, and Thomas presenting her with a Christmas dinner. Thomas implies that he loves Angela despite her many sins. Despite Angela's pleas and threats, Thomas continues to hold her there against her will, even forcing her to call her family and lie about an illness so that no one will come looking for her and while he is unlocking her chains, she drives a fork into his back, but is unable to escape.
Handcuffing her wrists together behind her back, they climb into his car and drive down to P4. There, they find a fellow coworker, Jim, tied to an office chair. Thomas rams Jim into the wall with his car multiple times, causing his intestines to rupture out of his body and ultimately killing him. Amidst the murder, Angela is able to escape from the car.
Angela runs to the elevators with Thomas right behind, and enters. Thomas then flushes her out by flooding the elevator with a fire hose from a higher floor. When the elevator finally reaches the next floor it bursts, open spilling Angela and Karl into the hallway.
She breaks open an emergency fire axe and begins to destroy the cameras one by one while making her way to his office, prepared to fight. Once entering, she finds video playing of Thomas groping her body while she was drugged, and, blinded by her fury, she smashes the TV with the emergency fire axe. Thomas then appears and ambushes Angela with a taser.
Angela awakens, realizing she is locked in the trunk of her vehicle. She breaks out and encounters Thomas and his attack dog at the door. He releases Rocky (the dog) on her,she kills the dog with a tire iron.
On her way to the exit, she is suddenly side-swiped by Thomas in another vehicle, leading up to a game of chicken in which Angela wins. However, in the heat of the chase, Angela flips the vehicle and is presumably knocked unconscious. Thomas opens the door, Angela(faking her injury), manages to cuff Thomas on the car. She sets the car ablaze.
With Thomas dead, Angela limps onto the snowy streets of New York City, and towards the lights of several ambulances, finally coming to her aid.