The film commences with three siblings, all in their late teens to early twenties, gathered in a bathroom intently listening to a cassette tape. This tape imparts four critical words for the day: Sea, motorway, excursion, and carbine. However, the definitions provided appear entirely disconnected from their actual meanings. Once the tape concludes, one sibling proposes a challenging game, attempting to keep their fingers submerged in hot water for as long as possible.
As the narrative unfolds, we learn that the father has brought Christina, a female security guard familiar from his workplace, to the house, seemingly paying her to engage in sexual acts with his son. This sordid encounter feels utterly mechanical and forced. Afterward, the father drives her back while blindfolded to preserve the house's secrecy.
The family's day-to-day existence becomes increasingly evident, revealing that the children have no connection to the outside world. They are indoctrinated into believing that they cannot exit the main gate unless they lose a dogtooth—which are, in truth, permanent. To bide their time, they assist with household chores, partake in various endurance games, and watch recordings of themselves. Good behavior is rewarded with stickers, while poor behavior incurs physical and verbal punishment. Adding to their distorted reality, they are led to believe that a brother once attempted to cross the fence but was met with dire consequences and thus, they frequently try to communicate with him.
The father’s interactions extend to a dog training facility where he learns that their dog is still in training and cannot be retrieved yet. Christina’s visits continue, but her patience wears thin when the son refuses to engage with her, leading her to find solace in sexual encounters with her elder daughter, offering trinkets like a hairband in exchange. This dynamic gives rise to the elder daughter also seeking out similar exchanges with her younger sister. Both seem to find enjoyment in these interactions, a stark contrast to the son's reluctance.
One fateful day, a stray cat wanders into the garden, bringing terror to the siblings. The son, however, takes matters into his own hands and kills the cat. When the father returns, clad in fake blood, he spins a tale of how cats can be sinister, claiming that the family’s brother on the other side of the fence was murdered by one. This grim narrative prompts a ceremony for their "deceased" brother.
Things take a twist when the mother reveals her pregnancy with twins, sparking discontent among the children who realize sharing their already limited space will be inevitable. The father, in response to their complaints, suggests reconsidering the additions should the children show improved behavior.
In another turn of events, the elder daughter persuades Christina to lend her two Hollywood film tapes with the promise of returning them. After viewing them, she begins to mimic the films, incorporating quotes into her daily life and even adopting the name "Bruce," possibly inspired by Jaws. When the father discovers the films, he reacts violently, punishing her brutally. Following this, he confronts Christina, attacking her in a rage over the perceived negative influence these films might impart to his own children.
As things escalate, the parents decide to shift the responsibility of choosing a new sexual partner for their son upon him, leading him to select the elder sister. Her discomfort shines through as she resorts to quoting lines from movies during their encounter to express her unease.
At a celebratory dinner for the parents' wedding anniversary, the children are called upon to perform a dance. The younger sibling tires and sits out, but the elder finds joy in replicating dance moves from Flashdance, only to be interrupted by a visibly concerned mother.
In an impulsive moment, the elder daughter uses a dumbbell to knock out one of her dogteeth and subsequently sneaks outside, hiding in the trunk of the family car. Panic ensues when the father discovers the tooth and blood, frantically searching for her. As the urgency mounts, he leaves the premises, pressing the family members into a growing state of despair over her absence.
The following day, the father heads to work, leaving the car unlocked in front of the factory yard. The camera lingers on the trunk, which remains stubbornly shut, leaving the fate of the siblings hanging in the balance.
