Note: This is a remake of the 2010 Spanish-language low-budget Uruguayan horror film 'La Casa Muda'. Both the original and this remake were (allegedly) shot in one take with no actual cuts or edits with a single camera, similar to the 1948 experimental film 'Rope' by Alfred Hitchcock.
We begin with an overhead shot of a young woman, Sarah (Elizabeth Olsen) sitting on some rocks in a lake. As she gets off and begins to hop among the rocks back to the shore, the camera descends and begins following Sarah in real-time. She walks up to an obviously dilapidated house. The house is three stories tall and has red-brick exteriors with all of the windows boarded up. Sarah's father John (Adam Trese) meets her near the front steps and tells her sternly to pick up the gardening tools lying about. John then asks Sarah about her Facebook profile, and she admits that her ex-boyfriend may want to get back together with her, much to John's disapproval.
John's younger brother and Sarah's Uncle Peter (Eric Sheffer Stevens) walks through the front door and greets the two of them. He says that there is a big problem in the house. They walk in, and though it is daylight outside, the house is almost pitch black as all the windows are boarded. The trio turn on their electric lanterns and follow Peter to the dining room (the source of the problem) where John hits the wall with a sledgehammer to reveal that mold has grown within the walls, and maybe throughout the entire house. Tools and clutter are strewn everywhere. They take a picture of the mold with their polaroid camera and after her father walks out of the room Peter stares at Sarah, telling her how beautiful of a woman she has become. After they enter the living room, John and Peter then leave to go into another part of the house, and Sarah starts up the stairs when she hears a knock at the front door.
She opens the door to see a girl roughly her age standing on the porch. The girl gives a loving hug to Sarah and introduces herself as Sophia (Julia Taylor Ross), a childhood friend who lives in the town. Sarah says she honestly doesn't remember Sophia since it has been so many years since she has been to this house, and Sarah also jokingly states that she has holes in her memory. None of this deters Sophia from eagerly recounting the times they played together as kids. Sarah tells Sophia that she did not go to college and works with her dad restoring houses until she figures out what to do with her life. Sophia asks Sarah why all of the windows are boarded shut with plywood, and Sarah explains that after the house was abandoned, drunk squatters lived there and broke every single window until the police forcibly evicted them. Sophia said that she tried to call, but Sarah tells her that the home phones are disconnected and Sarah does not have cell phone service so far outside of town. Sophia says she is glad she finally got to see Sarah again, and they make plans to meet up later that night to go out and continue to reminisce. As Sophia gets on her bicycle to leave, Sarah calls out that she does remember her. Sarah then returns indoors, once again locking the front door and returning the key to its hook, shutting out the daylight. Soon Sarah hears arguing between her father and her uncle. Her uncle complains loudly how stubborn John is and starts to leave the house in anger. But John stops him just to remind him to call the electrician to get the power restored.
After her father leaves the room again, Sarah lights two oil lamps and opens a beer. As she begins to take her first sip, she hears loud thumping and a dragging noise coming from upstairs. She immediately calls her dad, who says it is probably just rats, but Sarah insists that they check it out. The two go upstairs to the second level to investigate, and as a "joke," her dad slams open a door hard into Sarah's arm. They walk into the master bedroom, and some polaroids are lying out on the bed that John quickly picks up (before Sarah can see them) and stuffs them in a night table, saying that they are pictures of the repairs and saying that Peter never learns how to put things away. John then takes Sarah to the room she used to stay in when they used the house when she was a kid, and insists that she clean the entire thing out and trash whatever she doesn't want. Sarah is relatively calm in her electric lamplight and can hear her dad walking around taking care of things in other rooms. She looks through her clothing, which includes a ballerina outfit, and begins stuffing things in a trash bag. She comes across a locked red trinket box and throws it away. Soon she hears a loud banging on the wall outside her bedroom. She calls out to her dad, but he does not answer. A frightened Sarah begins to search the upstairs, calling out to her father but to no avail. As she leaves the bedroom the door slams by itself behind her and Sarah immediately panics and runs downstairs towards the front door, but the key is no longer on the hook. She then runs towards the kitchen door that leads outside, but finds it padlocked. She begins opening drawers to find the key, and in the background, a large, male intruder stands ominously watching her. She can't find the key, and the intruder is no longer there when she looks in his direction. As she continues to pace around, she hears heavy footsteps approaching and hides under the dining room table, accidentally knocking down her beer bottle. A male hand leans down to pick it up, and Sarah can just barely contain her screams. The figure walks out of the room and Sarah begins hyperventilating, until she notices the intruder's hand trying to grab her leg. She manages to squirm out of his grasp and runs upstairs to a room and locks the door, pushing a dresser in front of it to barricade herself in.
After a few moments Sarah calms down, and apparently, was not followed by the intruder. She begins trying to open the windows, but can't knock out any of the boards. As she searches the room for anything that can help her, a figure falls out from behind some drapes. Sarah screams loudly, but then realizes that the figure was her dad, who lies unconscious on the floor. She goes over to her dad and finds a huge gash on the side of his head. As she cradles him, she gets blood smeared over her shirt. John begins groaning, and Sarah is happy to find that he is still alive, though in bad shape. She knows that she has to get him some help, so she searches his pocket and finds a key. She listens to the door for awhile and hears nothing. She grabs her electric lantern, then pushes aside the dresser and exits the room to head for the exit.
She sneaks downstairs and tries to open the padlock on the kitchen door, but it does not work. Sarah panics once again and tries to knock of the lock, but soon gets a hold of herself again. Sarah soon comes to the sad realization that the key must belong to an exit located in the basement. She opens the basement door, and slowly descends the steps to the pitch-black basement. The basement is in total disarray, with tons of exposed pipes and machinery. It is clear that Sarah is unfamiliar with the basement layout as she keeps running into things. She opens a door to reveal what looks like a child's room that was recently used (the bed was unmade). At that moment, she hears loud, pounding footsteps descending the basement stairs. She hides behind the door to the room as the menacing intruder walks by, holding his own electric lantern. The intruder's search is unsuccessful though, and he soon is heard walking back upstairs. No longer able to keep her composure, Sarah runs throughout the basement, eventually opening a door to a storm-cellar with a padlock on the door leading outdoors. As she fumbles with the padlock, the footsteps hurry back downstairs, coming closer and closer. Sarah manages to finally unlock the storm cellar doors and flees outside.
Sarah runs in blind panic through a field and eventually hits the road. Finally having gotten a decent distance from the house, she stops in the middle of the road to catch her breath. As she turns around to look behind her, she sees a spectral young girl staring at her from the bushes. She screams, and as she does, a truck almost hits her. It is her Uncle John, returning from town. She leaps into his truck and he says he did not see any girl and demands to know what happens after he notices the blood on her shirt. She explains that an intruder has infiltrated the house, and Peter insists that they go back to the house to get John despite Sarah's protests and they begin driving back to the house.
They arrive, and Peter pulls out his gun from the trunk and locks Sarah into the car as he goes inside to retrieve John. Sarah sits there, waiting for Peter to return. She looks in the rear view mirror and sees the warning that the lift gate is open. Sarah begins crying once again and returns her gaze to the mirror where she sees the trunk opening and the intruder standing behind the car. She flees the car and runs into the house, and slams and locks the door (with Peter's key) behind her. Peter immediately runs to her and says it is impossible for anyone to have opened the trunk as he has the car keys in his pocket. Nonetheless, she insists that they stay together, and after Peter calms her down, he asks her to show him where she left John.
They go back up to the second level and into the room where Sarah left John. Unfortunately, John is no longer there, all that remains is a small pool of blood. Peter is clearly upset and they begin searching around. Peter opens a closet and finds more polaroids, but like John before him, he quickly grabs them and throws them into a trash bag. Peter had apparently searched the basement before Sarah ran inside, so the only place left is the third level attic-type area. They go upstairs and hear that a generator mysteriously starts up. They enter a room where a pool table is stored and follow the sound of the generator. The polaroid camera is sitting on the pool table. They sneak up to a tarp hanging like a curtain on the wall and rip it open, but nothing is behind it except for the generator. Suddenly, the generator goes out, and since Peter had turned off the flashlight when they went upstairs, the two are plunged into darkness. A loud thump is heard. Sarah manages to grab the Polaroid, and begins snapping pictures to light the room with its flash. She sees the little girl standing in the doorway and in the next flash sees the intruder right in front of her and he grabs for her. She ducks under the pool table. Eventually the generator springs back to life illuminating the room. Suddenly, Sarah begins having a vision. There are two pairs of men's legs walking around the pool table. They are taking pictures of something on the table and one of the men is saying things like "see, that wasn't too bad" and "it was a fun game." She then sees a pair of legs belonging to a little girl drop over the edge of the pool table, and one of the men help her down. Sarah sees that the little girl is clothed in a tutu, and the man says to her that they can now go get a snack. Suddenly Sarah is snapped back to reality and sees her Uncle Peter being dragged out of the room. Sarah crawls out from under the pool table and finds Peters gun, then slowly begins to follow Peter's dragging body.
Once the intruder and body are around a corner into another room, she works her way slowly down the stairs. But at the bottom of the stairs the intruder is waiting for her. She fires the gun but misses, then runs into the master bedroom and hides under the bed. She hears a creaking noise coming from next to her and when she turns her head she finds the spectral girl also hiding under the bed. The girls puts her finger to her lips and shushes Sarah just before she is violently dragged out from underneath. Sarah flees from the bedroom into the bathroom and locks it. She hears noises from the bathtub and pulls open the shower curtain to find the spectral girl sitting in a tub of water with empty beer bottles and pouring water out of the beer bottles onto herself. Sarah turns her head away from the little girl and sees blood seeping out of the toilet. When she turns her head back to the girl she the water has turned to blood and now the toilet is overflowing with blood. Suddenly a sledge hammer breaks through the wall to the bathroom. She runs into the joining bedroom where she sees black mold covering the ceiling and walls. The intruder steps into view with his arm around the little girl. Sarah can't take any more of this and runs in full panic down the stairs, smearing blood on the wall from her hand on the way down.
She sees Sophia in the foyer scantily dressed, and she tells Sarah that she has been looking for her because they had a date. Sarah runs for the door and frantically searches her body for the key. Sophia walks toward Sarah holding up the key and asks if that what Sarah was looking for. She places it in Sarah's hand but it isn't the right key for the front door and Sophia comments that the front door is not the way out. Sarah follows Sophia into the dining room, where John is sitting in a chair wrapped in plastic. Sarah rushes to him and begins to rip the plastic off and sees that he is also bound with tape. Sarah turns to Sophia, who is standing nearby with a drink in her hand, and frantically asks what she did to him, where Sophia replies with "Not nearly enough". Sophia saunters over to Sarah and says that Sarah needs to remember what happened and plug up the holes in her memory, and then slides the red trinket box on the table towards her. Sarah opens it with the key that was handed to her and finds a polaroid photo of herself as a young girl. Sarah turns her head and looks at a nearby window, and sees that her reflection is of the little girl. When she turns around she sees the intruder dragging her uncle's body into the dining room, then the camera pans upwards to the intruders face and it is actually Sarah who was dragging the body. She drops the body and turns to Sophia and asks if any of this was true and if she did indeed do this. Sophia then walks toward Sarah and hands her a knife, telling her to finish the job. Sarah lashes out at Sophia instead, slashing Sophia on the hand. Sophia responds angrily, telling Sarah to stop punishing herself. Sarah looks at her hand to notice it is slashed in the same place she slashed Sophia's hand, and when she looks up Sophia is no longer there.
Sarah begins walking towards her dad who is now fully conscious. She rips the tape off of her dad's mouth, holds the knife in front of his face and shushes him, telling him to be quiet or mommy will wake up then she would have to punish him. She straddles him and forces him to drink an entire beer bottle while telling him to quit being such a baby because it is just a game. She then jumps off of him and starts sobbing and saying how much it hurts and says: "why daddy... did you do such a thing?". John tells her that he (daddy) would never do such a thing. She screams that he is liar and throws the polaroids at him. He tells her that she is the one who attacked him and Peter just now and that she is remembering things that never happened. He promises to help her with her psychosis if she will just let him go. Sarah approaches with the knife, and uses it to unbind John's hands. He then takes the knife and cuts away the straps to his legs and stands looking at a weeping Sarah. He drops the knife to the ground and goes to embrace her, saying none of this is her fault. He then punches Sarah to the ground and takes off his belt and begins whipping Sarah with it. Suddenly, he hears Peter telling him to leave her alone. He turns around to find a semi-conscious Peter on the ground. John tells him to shut up and says that he always enjoyed the show. Peter grabs for the knife on the floor and John kicks the knife out of Peter's hand calling him a loser. As he turns back to Sarah she swings a sledgehammer into his abdomen, knocking him to the ground. She raises the sledgehammer above her head, and brings it down hard on John killing him. She then begins advancing on Peter, who begins crying and apologizing for not stopping her father and says that he never meant for things to get so out of hand. She stands over Peter, but then drops the sledgehammer beside him. Peter lays there crying, and we see a pool of blood near John's lifeless body. Sarah unlocks the front door (having the key the entire time?) and walks out of the house and into the night, leaving it behind.
(Post note: In sum, it appears that Sarah was actually the intruder the whole time, and that similar to the film 'Fight Club', split her personality into the active intruder and the passive victim, and the viewer saw events from the point of view of the peaceful/victim personality (although how she could have done everything in the film herself is a mystery). The little spectral girl was clearly the manifestation of Sarah's childhood self who was abused by her dad, and possibly/likely by her Uncle too. It is harder to determine whether Sophia was a real person whose visit triggered Sarah's repressed memories of abuse (and perhaps was abused as well) and later hallucinated by Sarah as some sort of safe harbor or was merely another physical manifestation of Sarah's fragmented personality the entire time.)