NOTE: This spoiler was sent in by Andrew K!
Movie begins with Christmas music playing in the background while the camera pans through a parking garage ending on the P2 sign. We keep going along with the music until the camera pans into a small car parked on that level. It zooms in on the keylock for the trunk and suddenly it pops out and an eye is looking out. The truck is popped and a woman in handcuffs sits up.
Flashback to the beginning and how we got here.
Angela is a corporate woman, too busy for a romantic life or any life for that matter. She is in the office working on Christmas eve and is on the phone, promising her sister she will surely be there for her Christmas party. She finishes up the phone call when a man walks in and looks around rather suspiciously. He tells her over and over again "how sorry I am" for what happened at the Christmas party between them. He tells her that with being a new father and being drunk, he didn't mean it, etc. (IMPORTANT LATER) and Angela tells him it is okay. Being the last one to leave, she finishes up her paperwork and turns the corner into the building security guard who tells her he thought he was alone in the building. She finishes what she needed to do and takes the elevator down with the building guard to the lobby where she tells him Merry Christmas and heads down to the parking garage elevator. Walking to her car, she tries to start it, but it will not go. In desperation, she heads back up to the lobby, but the Building guard is nowhere to be found. Using her cell, she calls a taxi and then her sister to tell her she is running late with car problems but will be there. The taxi shows up, but she is unable to leave because the doors are locked and she cannot get out. Heading down to the parking garage, she heads for the exit only to find it locked as well as the taxi drives off.
She goes to the parking garage security office and opens it as a large dog comes at her, growling and biting toward her, but chained up. The parking garage guard, Tom, comes around the corner and tells her the dog is always that way. She tells him about her car troubles and he offers to go take a look using a battery jumper. He attaches it to the car and they try and get it to start, but to no avail. Finally, she thanks him for his time after his repeats of "I'm just trying to help you."
Leaving the security guard's office, she begins to walk back toward the lobby door as the lights begin to go off on her, leaving her in total darkness. At this point she freaks and begins to run, using only the light from her cell phone to guide her. She stumbles and falls and as she stands, you can see Tom behind her with a handkerchief with presumably chemicals in it as he grabs her from behind and holds it to her mouth saying, "It's okay. I just want to help you." As she fades out.
She wakes to find herself chained by the ankle to a table in Tom's office which has been decorated for a Christmas dinner and wearing a white low cut dress. Tom has obviously been infatuated with her as he begins to talk to her, telling her he just wants to get to know her. She tells him she has a boyfriend who will be coming to look for her. Tom asks if her boyfriend lives with her. She says yes.
He nods, saying, "Then he's your fiance isn't he?" She nods and he asks what he does for a living, his name, and how long they've been seeing each other. She responds that he is a newspaper journalist for the sports department. Tom doesn't buy it since he says he reads that paper and the name doesn't ring a bell and she is a good liar.
Tom brings her a phone and tells her to call her sister (he names off her relatives to prove he knows a LOT about her) and tell her she won't be coming for dinner. He puts it on speaker so she can't try anything. Angela is crying by this point, but does as she is told, tell her sister she came down with the flu. The sister only responds "Quit thinking about yourself for once." The mother comes on the phone and tells Angela to just take care of herself as they hang up. Tom thanks her saying, it was the best Christmas gift he ever got before telling her he has one for her. He pulls out a videotape and plays it. It shows Angela and the man who had apologized to her in an elevator. The man is obviously drunk and trying to grope her before she storms off the elevator.
Tom tells Angela he wants to show her something and begins to unlock the chain and handcuff around her ankle as she stabs him in the shoulder with a fork, trying to make a break for it, but Tom is too quick and handcuffs her hands behind her back. He says they are going for a drive. He puts her in his car and they begin driving to the lower levels until they are in the basement. She asks why they are here and he says to get her respect. In front of them, taped to a chairs with wheels is the man who was in her office apologizing for his actions at the Christmas party. Tom stops the car and hands her his nightstick telling her to go give him what he deserves for treating her like a slut. She says no. Tom keeps going on and on about how he had no right to touch her like that. She refuses again as Tom nods, saying, "You're too good for that. I'll do it myself."
He goes out and proceeds to pummel the man with his nightstick while Angela fumbles with the door handle trying to get out. Tom leaves the man bloodied as he gets back into the car and backs up before pulling up to beside the chair and beginning to push it toward the far wall. He rams into the man three times, finally exploding the man's head all over the windshield.
Angela manages to escape out the door at this point and heads for the upper level. She stops to twist her body so her hands are in front of her. She heads for Tom's office and finds her cell and his keycards for the door locks. Taking them, she runs to the only area near the exit where her cell has a signal and manages to dial 911 before she drops the phone out of reach. She screams that if anyone can hear her to come and gives the address. With Tom approaching, she heads to the elevators and begins to go up as Tom is beginning to catch up. She stops the elevator mid floor and tells Tom via the elevator phone that she's going to wait there and he can't get her.
Tom drops the firehouse down the elevator shaft and begins to fill the elevator with water and eventually tosses the body of the Building Guard down crashing through the roof. She has no choice but to go down and open the elevator doors as water gushes out and she is on the run again.
Again, she heads for the office trying to find safety, but Tom ambushes her and uses his stun gun on her and places her in the trunk of her car. The police arrives and he plays like he doesn't know what is going on and that all is quiet. They look around for a while, during which Angela awakens and begins to try and break out of the trunk using her crowbar. This leads to the opening scene as she pops the trunk and jumps out, running after the police as best as she can. As she gets there, Tom is just shutting the garage door behind them. He has his dog, Rocky, on the leash and as she runs, he unleashes him on her.
Running to another level, she breaks the car window of a rental service car and hides in the car. The dog attacks and she kills it with the crowbar before heading into the rental car office and dialing 911 and being stuck on hold. During her hold time she rummages through the keys of the rental cars and grabs one with an alarm. Grabbing a letter opener, she begins to try and undo her handcuffs.
Tom finds the dead dog and freaks saying, "Why did you do this to a poor defenseless animal? You killed my dog!" Then he proceeds into the office to look for her. He picks up the phone with the 911 operator on it saying, "Can you hear me? Tap the phone if you need help." As he hangs it up.
After hiding in a closet, she sets a trap for him as he opens another door. Leaping out, she sprays cleaner into his eyes and makes a break for it using a set of rental car keys to get into and drive off in a car. As she is starting it, Tom begins heading toward her. As she is approaching the exit, Tom rams her car with his own and forces her back. At the end of the ramp, they have a face off with her strapping in before they play a game of chicken with him swerving to miss her. She keeps going, but takes the turn too swift and flips the car.
As he approaches her, it seems as though she has been knocked unconscious and as he flips her up, she slams the letter opener into his eye. He drops the stun gun and they begin to struggle before she is able to handcuff him to the car handle, get his set of keys and get out of the way. As she begins to walk away, he yells out that she is nothing but a little slut. She stops and turns to look at him. Fuel is leaking from the car wreckage as she bends down and picks up his stun gun before saying, "You wanted to help me, let me help you." and she activates the stun gun into the fuel starting a fire that engulfs him before hitting the car and destroying it. She is finally able to leave using Tom's set of keys and the movie ends with her walking into the freezing night as a fire engine, ambulance and cop cars are approaching. The screen goes black as a voice says "Lady, are you okay?"
After spending a long Christmas Eve working at her office, and before she can go home to a family Christmas party, Angela Bridges (Rachel Nichols) finds her car won't start, and that her cell phone doesn't get reception in the building's underground parking deck she is in.
A kind and helpful security guard, Thomas (Wes Bentley), shows up and tries to fix her car, and when this is unsuccessful, calls her a cab. When Angela tries to leave the building, she finds the front door locked, and refusing to wait, the cab driver shrugs and leaves. When Angela goes back to the parking deck to tell Thomas what has happened, all the lights are shut off, the doors are chained shut, and the once-sweet Thomas knocks out and abducts Angela.
Angela discovers that the deranged Thomas has been stalking her for three years, and believes that they are "meant to be". As a "Christmas present", Tom murders Bob, a fellow employee of Angela that sexually harassed her in the beginning of the film, and Karl, another of the building's security guards that Thomas feels got "too close" to Angela over the years.
Angela escapes, and after evading him, trying to call for help, escaping a water-filled elevator (Tom uses a fire hose for this), and killing Thomas' attack dog, Rocky, a brief car chase ensues. Angela wrecks, and when Tom gets out of his car to help, Angela stabs him in the eye with a nail file and handcuffs him to the car door as gasoline from the wreck spills all over the parking lot. Angela is only ready to walk away, but when Thomas curses at her, Angela decides she has had enough and, wishing Tom a "Merry Christmas!", sets the gasoline on fire with a stun gun, leaving him to burn in the car.
Using Thomas' keys, Angela finally escapes the parking deck and runs into the fire department just as they are responding to the alarm.
Thanks for the Moviepooper - Daremaster Spoodle!