A group of friends (Simon, Danny, Gwen, Tyler, and Wendy) buy a house. They collectively asked a week off to move in and celebrate. The house is 2 stories high, main floor and upper floor. When they moved in, one of them (Simon) checked the upstairs first and found a locked room. Two other friends who checked the place before buying it say it wasn't there before, but simply accept that they may have forgotten about it.
The next day arrives, and they begin their celebration. One of the friends (Danny) leaves to buy things while the others start. Gwen goes upstairs to change since she plans on taking pictures. She notices the locked door is ajar. She enters the room. It is an empty room lined with closets and a small table with a key on top next to the door and a door on the opposite end. She calls for the others as she searches the room. It is empty. She opens the door on the other side. It leads her to a balcony with a scenery. The others come shortly after, and they enjoy the view for a minute before returning. However, when they reenter the room, the door is closed. After a brief argument, Tyler sees the key and uses it. There is a feint echo of the key turning and unlocking the door. Wendy is the first to rush out from fear. Gwen decides to shower since she believes she has tracked dust from the unknown room. Tyler goes to find Wendy, and Simon goes downstairs to prepare the food.

Once Gwen finishes her shower and is changing, lights outside dim. She assumes the clouds have decided to roll in. This allows a light shine through the keyhole of her door. At the same time, this occurs to Wendy's room as Tyler's voice fades, and when Simon walks into the pantry and the door closes behind him.

They ignore it since they all believe it is a natural occurrence. Once they finish their business and return to their doors, the light is no longer there. They open their corresponding doors and enter their "private" space. It is essentially the house, but darker, and they are alone. Aside from themselves, they are only able to hear muffled sounds made by the others. Using auditory hints to locate each other, they open a series of doors. The more doors they open, the more the rooms they enter become distorted.

While this occurs, Danny returns. He knocks on the door, and no one answers. He steps back and calls out to his friends. No reply. He assumes they are asleep. And feels bad and betrayed since it is a sunny day, and they agreed they'd prepare for the party. Danny searches for the house key and realizes he forgot it. He peers through the key hole and sees an empty house. He calls out once more, hoping he'd get an answer

Silence.

He searches the premises to see if their is a spare key lying around. There is. It is hidden in a lamp. Unbeknownst to him, it is the same key his friends have found in the unknown room. He uses the key and enters the house. Because of the eerie silence, he blocks the door from closing. He searches the house, finds no one, and ends up in front of the unknown door. He tries the door knob and it is locked. So, he tries the key, and it works. He opens the door. It creaks as it slides across the floor. Inside the room stands a black cloth, assumingly a mannequin that is covered. He calls for his friends and tries to laugh it off as a prank. He approaches the clothed figure. As he does, he hears the door creak as it begins to shut. He runs for the door and makes it in time before it closes. Just as he is about to open the door, he gets dragged away.
His friends, in their respective dimensions, hear his muffled screams for help, causing them to panic.

As they continue to open doors and run away from whatever is with them, they start to see a pattern. At first, they think the patterns lie in the shifting of rooms as if the area behind the doors are rotating. This is somewhat debunked as they simply further themselves into darker areas. Luckily, this also gives them another hint. The light from the keyhole becomes more evident. Unfortunately, that also becomes a lure for whatever thing is with them.

One by one, they are hunted down.