Walled In is a 2007 Canadian horror-thriller film directed and co-written by Gilles Paquet-Brenner and starring Mischa Barton, Cameron Bright, and Deborah Kara Unger. The film is based on the best-selling French novel Les Emmurés by Serge Brussolo. It is Paquet-Brenner's English-language film debut.

The film opens when a little girl, Julie (Sophi Knight), wakes up to find herself in a small concealed room, confused at what is happening. When the room starts filling with cement from all corners, the girl cries for her father, but the cement only continues to rise, and eventually she is buried alive.

Fifteen years later Samantha "Sam" Walczak (Mischa Barton) is a recent engineering graduate. At her graduation party, her father, the owner of a demolition company, gives her a gift: a job supervising the demolition of a building in the middle of nowhere. If she is successful, she will become his partner. Sam arrives at the Malestrazza Building, and is greeted by Mary (Deborah Kara Unger), the caretaker. Sam tells Mary she will be staying in one of the apartments in the building. Jimmy (Cameron Bright), the caretaker's teenage son, takes her bags to her apartment, previously owned by Julie, and explains the rules of the building: she is to stay off the eighth floor because it is Malestrazza's and the roof because it is too dangerous.

Sam researches the building and discovers that it was the scene of a horrible series of murders where sixteen people were entombed in the walls. Jimmy takes Sam to the eighth floor and tells her how his father was one of the victims, the crime being blamed on a local factory worker. The lights go out, and Sam cuts her leg after panicking in the darkness. Later, Jimmy washes her wound and begins to caress her thigh, but she tells him to stop. Sam begins having nightmares about being entombed in the walls.

Sam's boyfriend arrives, causing Jimmy to grow jealous. While exploring the eighth floor, Sam and her boyfriend discover a secret passage which would allow someone to secretly view any of the apartments. Sam realizes that Jimmy has been spying on her. Later, as Sam and her boyfriend make love, Jimmy watches from behind the walls. The next morning they find his dog butchered. Sam and her boyfriend agree to leave.

Jimmy gives Sam a copy of the journal of Joseph Malestrazza, the building's architect. Sam realizes from reading the journal that there must be a large, open space in the center of the building. Jimmy goes to the roof to look for an opening to the hidden space. When he does not return, Sam and her boyfriend follow. They discover a massive shaft in the center of the building. They hear Jimmy calling from down in the shaft, saying that he is hurt. Sam has her boyfriend lower her into the shaft on a rope, but he is shot and killed, causing Sam to fall to the bottom. Jimmy then mails Sam's demolition report and sinks her car into a lake.

Sam awakens at the bottom of the shaft and discovers that a man is there with her. He is Malestrazza, the architect, who has been trapped there by Mary. He tells her that Jimmy is keeping her down there until she learns to love him. While trapped, Sam learns that Malestrazza orchestrated the murders as a form of human sacrifice, citing the fact that, of the Seven Wonders of the Ancient World, only the Great Pyramid of Giza is still standing after thousands of years, because (he believes) it was the only one in which workers were killed and buried during its construction.

Among his victims were Mary's husband and daughter (Julie), which caused a vengeful Mary to imprison Malestrazza. He also tells Sam that Jimmy is nice, but can be very cruel and imaginative when he disobeys Jimmy's orders.