Kristen McKay (Liv Tyler
) and James Hoyt (Scott Speedman
) return to the remote summer vacation home owned by James's parents in the mid-hours of the night following a friend's wedding reception. After an episode between the couple when Kristen turns down a marriage proposal from James, they receive a knock at the front door. When they open the door, there is a young blonde woman standing there with her face partly obsured by a burnt out door light. "Is Tamara home?", she asks. "No, I think you have the wrong house", they tell her. The mysterious woman then walks off into the night. James fixes the door light and then leaves the house to go buy cigarettes and get his mind off of things.
Meanwhile, Kristen stays at the house alone. The blonde woman returns, asking for Tamara, but this time Kristen does not open the door; "You already came by here", she tells the woman, who responds with "Are you sure?". The smoke alarm goes off soon after, due to the fireplace being blocked, and Kristen pulls the alarm off the ceiling and it clatters to the floor. Someone begins banging at the door. Kristen, a little unnerved at the entire situation, locks the doors in the house, and calls James asking him to hurry back, when the phone line goes dead. Kristen plugs her cell phone in to charge it, changes into jeans and a flannel shirt, and then picks up a half-smoked cigarette. As she stands in the living room of the house, a man wearing a sack mask emerges from the hallway behind her, and watches her silently as she gets a glass of water. He then disappears.
Another barrage of knocks come from the front door, and Kristen sees the smoke alarm, which was previously lying on the floor, sitting neatly on the center of a dining room chair. She hurries to grab her cell phone, but it has been taken off the charger and is nowhere in sight. She hears something hitting the windchimes and making a dragging noise on the back patio, and she slowly, armed with a kitchen knife, walks toward the sliding glass door. She pulls the curtain back, and the man in the mask is standing there, and he slams his hand on the window. She screams in terror, and bumps into the phonograph in the living room, knocking the needle off track, which causes it to begin repeating the same phrase from a country song. Suddenly, the front door opens slightly, and Kristen approaches it. In between the crack of the door someone wearing a doll-like mask peeks her head through. Kristen closes the door, locks it, and hides in the bedroom, yelling for the strangers to go away. Suddenly, the vinyl album stops skipping, and footsteps come down the hallfortunately, it is only James, who is entirely unaware of what is going on.
The couple search the house, but find nobody, and James initially believes Kristen to be letting her imagination get to her. The couple see the blonde woman, now wearing a Dollface mask (Gemma Ward
), standing in the back yard, staring at the house. James then goes outside to the car to retrieve his cell phone, only to find the car entirely vandalized, and his cell phone stolen. Dollface touches the back of his neck as he is crouched down in the car, and runs off, only to reappear a few feet from the car. He tells her to leave, and Kristen pokes her head outside in concern. James turns to Kristen, and when he turns back around, Dollface has vanished. James returns to the house, and he and Kristen find his cell phone sitting on the piano with its battery removed. James decides it's time to leave.
They go outside and attempt to drive away in the car, even with its tires slashed, but a truck pulls up behind them, driven by a different unidentified woman, wearing a mask that resembles a pin up. The Man in the Mask (Kip Weeks
) appears in front of the car, and a dark-haired woman wearing a the Pin Up Girl mask (Laura Margolis
) rear-ends the car, as James and Kristen scramble back into the house. They find a shotgun and gun shells in the bedroom, along with the word "hello" written all over the bedroom window in red paint by the villains. They approach the front door with the gun, and the Man in the Mask begins to break through the door with an axe. They block the door with the piano, and James attempts to shoot him, but misses. They then hide in a room down the hallway, armed with the gun toward the open doorway.
James' friend, Mike (Glenn Howerton
), whom he called earlier, arrives at the house, and has a rock thrown through his windshield. He approaches the house, and hears country music playing loudly on the record player. He enters through the back glass door, just as Dollface emerges from the shadows behind him. He sees the house is a complete disaster, and he walks down the hallway as the music continues playing. The Man in the Mask appears behind him, holding up his axe preparing to strike. Just as the music stops, Mike steps in the doorway, and James fires the gun, striking Mike right in the head. He dies instantly, and after a few seconds James and Kristen realize they shot the wrong person. The villains paint "KILLER" on the back door to taunt James, and he heads to the barn outside to use a ham radio for help. He spots Pin Up Girl emerging from the barn, and attempts to shoot at her from down on the ground, but the Man in the Mask runs up behind him at full speed. Kristen soon follows, after she senses the presence of the Man in the Mask in the house. She falls, twists her ankle, and is unknowingly stalked through the front lawn by Pin Up Girl. Once she gets to the barn, she fiddles with the radio, but it is then destroyed by Pin Up Girl.
Kristen crawls back to the house, as Dollface sits on the swing set in the backyard and Pin Up Girl stands in front of the barn. Once inside, Kristen cannot find James, and the power goes out. The Man in the Mask then enters the front door, and Kristen hides in a pantry as he lurks around the living room. He leaves, and just as Kristen is about to slip out of the pantry, Dollface appears in the door's slit shutters, and smashes it through. She then pauses, and notices the engagement ring, and Kristen emerges from the pantry, while Dollface taunts her by spinning a butcher knife around on the counter. The Man in the Mask then enters the house, holding a defeated James by his shirt collar. Kristen runs to the bedroom, but the window does not open. The lights come back on, and she creeps back toward the hallway. Upon reaching the doorway, The Man in the Mask rushes toward her, slamming her head into the back wall of the hallway. She falls to the floor and he drags her down the hall. She is initially unconscious but soon begins to claw at the floor and the screen fades to black as she screams.
It is then daylight, and each of the strangers loom over Kristen and James, who are now tied to chairs in the living room; Kristen has been dressed back into her white gown. Kristen cries, and asks "Why are you doing this to us?", to which Dollface emotionlessly replies, "Because you were home". Each villain removes their mask, but the camera does not show their faces. The three strangers then take turns stabbing both James and Kristen, and then leave in their pickup truck. As they drive down the road, they stop to talk to two boys delivering religious pamphlets. Dollface gets out of the truck and asks for one, to which one of the boys asks, "Are you a sinner?". "Sometimes", she says, and when the children are out of ear shot, Pin Up Girl says quietly, "It'll be easier next time." The three strangers then drive off.
The two boys approach the house, and enter to find a bloody and disastrous scene. James lies on the floor, dead, and Kristen in the hallway having dragged herself a short distance away from the living room, her white gown saturated in blood. One of the boys approaches Kristen's body, and just as he is about to reach toward her, she grabs his arm and screams in terror.