15-year-old Tom is grappling with his family's recent move from London to a secluded house in the picturesque Devon countryside. His heart is heavy with nostalgia for his friends and the comforting familiarities of city life, while the dynamics within his family feel unsettling. His mother is nearing the end of her pregnancy, while his father works in the home-furniture sector. Tom shares an unusually close bond with his 18-year-old sister, Jessie, as they all come together to support their mother during her pregnancy.
One fateful night, as Mum goes into labor, Dad rushes the entire family to the hospital. Amidst the chaos of the drive, their car crashes—but fortunately, no one is seriously hurt. In the midst of this turmoil, a baby girl is born while Mum remains trapped in the vehicle. Afterward, the family heads to the hospital to ensure everyone's well-being and sees Mum joyful with her new baby. Later, while on a shopping trip with Mum, Tom expresses his loneliness and his longing for friends. His mother reassures him, saying that he will soon make new connections. However, upon arriving home, something unusual catches Tom's eye as he enters through the back door.
Determined to uncover the truth, Tom confronts Jessie about a shocking sight he witnessed: their father and Jessie, naked in a bathtub together. While Jessie brushes it off, Tom's insistence fuels his suspicions. At a family outing to a local pub, Jessie introduces Tom to her boyfriend Nick, who then drives the siblings to the beach for an uncomfortable evening under the stars. When Jessie and Nick vanish into the night, leaving Tom alone by the fire, the parents erupt in anger upon discovering their absence, with Mum needing to restrain Dad from taking drastic measures against Jessie. Tormented by what he suspects of Jessie's relationship with their father, Tom lashes out in frustration.
In a moment of curiosity and dread, Tom decides to follow Dad and Jessie as they claim to be going for a run. Armed with a video camera, he trails them to an old war bunker near the beach. Through a hole in the wall, he witnesses an unthinkable act: Dad violating Jessie against her will. Staggered by the horror, Tom walks away in anguish, ultimately discarding the camera into the sea as if to rid himself of the memories it contained.
In the aftermath, Tom accuses Jessie of being complicit in their father's actions, and while she allows him to burn her breast with a lighter as a form of twisted solidarity, their emotional turmoil leaves them both unsatisfied. A trip to London follows, where Jessie encourages her friend Carol to seduce Tom, but the moment takes a sharp turn when Jessie walks in on them.
Amid escalating tension, one night Tom is roused by Mum who urgently declares they must return to the hospital due to the baby’s health concerns. Later, after Jessie drops Tom home, they encounter Lucy, a figure who offers Jessie comfort but harbors secrets of her own. Distraught, Tom hops on his bike to return to the hospital, where he witnesses blood in the baby’s nappy, igniting his fear for his younger sister. He implores Mum to keep Dad away from the baby before storming out, feeling unheard.
Later, Dad confronts Tom, claiming he has received a call from the hospital, insisting Tom's allegations are fabricated. In a violent showdown, he physically assaults Tom, who protests that he is not the one disrupting their family. Jessie, caught in the crossfire, can only cover her ears in distress.
In a moment of desperation and clarity, laying beside each other in bed, Tom and Jessie share a fragile connection as she thanks him for standing up to their father. They confront Dad together upon his return, with Jessie backing Tom’s claims, yet they are met with further gaslighting. Tom realizes their father’s inability to change and, in a surge of rage and self-preservation, he stabs Dad in a fit of desperation.
As Dad writhes on the floor, gasping for air, Tom and Jessie watch in shock, realizing the gravity of their choices. Tom flees to the bunker, seeking solace, with Jessie following silently, leaving them in the haunting aftermath of their irrevocable decisions. As they sit close together, Tom ponders their future, moving to close the door of the bunker behind them, ready to face whatever comes next.
