sinister

The film opens with Super 8 footage depicting a family of four standing beneath a tree with hoods over their heads and nooses around their necks. An unseen figure saws through a limb acting as a counterweight, causing their deaths by hanging.

Months later, washed-up true crime writer Ellison Oswalt (Ethan Hawke) moves into the murdered family's home with his wife, Tracy (Juliet Rylance), and their two children, Ashley 7 years old (Clare Foley), a gifted artist who is allowed to paint on her walls, and Trevor 12 year old (Michael Hall D'Addario), who begins re-experiencing bizarre night terrors upon moving into the home. Only Ellison is aware that the house they are moving into was the crime scene. Ellison intends to use the murders as the basis for his new book, and hopes that his research will turn up the fate of the family's fifth member, a 10 year old girl named Stephanie who disappeared following the murders.

Ellison finds a box in the attic that contains a projector and several reels of Standard 8 mm footage that are each labeled as innocent home movies. Watching the films, Ellison discovers that they are snuff movies depicting families being murdered in various ways: having their throats slit in bed (Sleepy Time '98), being burnt to death in a car (BBQ '79), being drowned in their pool (Pool Party '66), being run over by a lawn mower (Lawn Work '86), and the hanging that opened the movie (Family Hanging Out '11). The drowning film proves especially disturbing for Ellison after he notices the face of a demonic figure watching the drownings from the bottom of the pool. Ellison eventually finds the figure observing the murders in each of the films, along with a strange painted symbol; inspecting the lid of the box containing the films, Ellison discovers childish drawings depicting the murders, along with crude sketches of the demonic figure, identified as "Mr. Boogie." Consulting a local deputy (James Ransone), Ellison discovers that the murders depicted in the films took place at different times, beginning in the 1960s, and in different cities across the country. He also learns that the families were all drugged before being killed; and that a child from each family went missing following every murder. The deputy refers Ellison to a local professor, Jonas (Vincent D'Onofrio), whose expertise is the occult and demonic phenomena, to decipher the symbol in the films. Jonas tells Ellison that the symbols are that of a pagan Babylonian deity named Bughuul (Nick King), who would kill entire families so that he could take one of their children into his realm and consume their souls.

One night, Ellison hears the film projector running and goes up to the attic. There, he finds the missing children in various states of decay, watching one of the films. Bughuul suddenly appears on camera before physically appearing before Ellison. Ellison takes the camera and the films to the backyard and burns them. Then he wakes his family to tell them that they are moving back to their old house. At his old home, Ellison receives a message from Professor Jonas, who sends him scans of historical images associated with Bughuul; each drawing had been partially destroyed by the early Christians, who believed that images of demons served as a gateway for them to come from the spiritual realm to the mortal world. Ellison then discovers the projector and films in his attic, along with a new envelope of film labeled "extended cut endings". During this time, the deputy tries calling several times, but Ellison never answers. The next time the deputy calls, while Ellison is assembling the films, he answers. The deputy informs him that he has discovered a link between each of the murders: Every family had previously lived in the house where the last murder took place, and each new murder occurred shortly after the family moved into their new residence; by moving, Ellison has placed himself and his family in line to be the next victims.

Ellison then watches the footage. He finds that it depicts the missing children coming onscreen following each murder, revealing themselves to be the killers before suddenly disappearing. Before he can react, Ellison becomes light-headed; inspecting his coffee cup, he finds a note reading "Good Night, Daddy" and a green liquid inside the cup before losing consciousness. Ellison awakens to find himself, his wife and his son bound and gagged. Ashley approaches holding the 8 mm camera, and promises him that she will make him famous again. Ashley then proceeds to brutally murder her family with an axe, using their blood to paint images of cats, dogs and unicorns on the walls. Her work complete, Ashley views the Super-8 film of her murders, which concludes with an image of the missing children watching her. Bughuul appears, causing the children to flee. He then lifts Ashley into his arms and disappears into the film with her.

The film concludes with an image of the box of films in the Oswalt family's attic, now accompanied by Ashley's reel, labeled "House Painting '12". Bughuul appears as the screen cuts to black.