Judith King lives with her father Andy King, mother Sheila King, and brother Joe King in Yorkshire. She uses the camcorder gifted to her by her father to document her everyday life and her family, and she harbors a private crush on Claire, a teenage girl across the street. She is a lesbian and has not yet come out to her family, often spying on Claire and filming her from the bedroom window.
On a trip to see their new house, Judith tries to persuade Andy King not to move, but she struggles to tell him about her feelings for Claire.
[Andy King] is chasing a promotion, yet financial strain and mounting pressure at home push him toward erratic behavior. One night he comes home covered in blood and claims that his colleague Ray has suffered a facial injury. It seems unlikely that he’ll secure the promotion or sell the house, amplifying his distress. Sheila and Joe begin to clash with him more frequently.
In a tense moment, Judith hides in the garden while Andy lunges toward her; she screams and races back inside, locking the bedroom door.
The tension spills into daylight as Andy impulsively builds a new swimming pool and the family hosts a pool party during an open house. An uninvited, disfigured Ray arrives, angry and ready to lash out, and Andy escorts him outside. Judith secretly records their confrontation. Ray accuses Andy of lying about his career prospects, claiming Andy stole the promotion from him. The confrontation reveals that Andy has fabricated parts of his story, and Ray’s version of events casts Andy’s integrity into doubt. Later, Andy discovers that Judith has been documenting his increasingly unstable behavior.
With finances still tight, the Kings decide to stay in their old home rather than move into the dream house. Sheila returns to work while Joe and Judith continue with school. Andy investigates the house and uncovers painful truths: Sheila’s favoritism toward Joe, rooted in a post-natal depression she suffered; Joe’s hidden stash of drugs; a video of Joe receiving oral sex; and a secret shrine to Claire built by Judith. On camera, Andy admits that he was the one who hurt Ray in a bid to secure the promotion while Ray was incapacitated.
That night, a smoke alarm awakens the household, and Andy locks all doors and windows. He lays bare the full extent of the family’s dysfunction, including Judith’s crush on Claire, and demands a drastic choice from Sheila and Joe—either they leave with him or he will leave them.
The next day, Judith returns from a visit with Claire to find her father in a state that suggests he may attempt suicide. In a devastating escalation, Andy chokes Judith as she tries to reach out, then murders Joe. Sheila comes upon the scene, horrified, only to be killed by Andy as well. A broken man, he sobs about being reunited with his family. He collapses the camera onto the floor, and the footage shows that Judith is still alive, though her fate remains unclear as he destroys the device.
The scene then shifts to a beach moment with the family together, a haunting image that is abruptly interrupted when Andy notices the camera and turns it off.
