A news segment captures the harrowing aftermath of boys recovering in a burns unit after playing with fireworks, leading one of them to insist he would continue engaging with them.
Nitram is a young adult with intellectual disabilities residing in Port Arthur, Australia, where he lives with his parents. He often delights in setting off fireworks, much to the irritation of the neighbors, and sells them to local schoolchildren. His father recently secured a business loan aimed at purchasing a bed and breakfast, a venture that would also require Nitram's involvement. In a moment of yearning, Nitram pleads with his mother for a surfboard upon spotting a captivating woman alongside a surfer, only to be met with her sharp refusal.
In a bid for financial independence, Nitram starts mowing lawns, which leads him to cross paths with his neighbor, Helen. A retired actress and heiress, she hires Nitram to walk her dogs, and their friendship blossoms. To his astonishment, Helen gifts him a car despite his lack of a driver's license and a troubling tendency to grab the steering wheel during drives.
As frustration mounts within his home life, Nitram announces his intention to move in with Helen. She permits him to stay in a spare room, provided he discards his air rifle that disturbs her peace. During a birthday celebration, Nitram introduces Helen to his parents, leading to his mother sharing a troubling story from his childhood where he took pleasure in causing her pain by pretending to be lost.
Even with the finances lined up for the bed and breakfast, Nitram's father faces disappointment when their offer is trumped by another couple. This drives him into a deep despondency. Seeking solace, Nitram proposes a trip to Hollywood with Helen, but during their drive to the airport, a harrowing incident occurs when he lunges for the steering wheel again, resulting in a tragic accident that claims Helen's life and leaves him severely wounded. In a moment of desperation, he deceives the police by claiming he was asleep when it happened.
Following the incident, Nitram finds himself the unexpected heir of Helen's deteriorating mansion and a substantial inheritance of over half a million dollars. In this vulnerable state, he succumbs to heavy drinking. His mother pleads with him to support his father, who has slipped into a deep depression. In a futile attempt to buy the bed and breakfast, he finds that the new owners are unyielding in their refusal. Tragedy strikes again when his father is discovered dead in a river under suspicious circumstances.
Appearing at his father’s funeral clad in an eye-catching electric blue suit and hat, he is barred from entry by his mother, who worries that his presence will bring embarrassment. Spiraling into isolation, Nitram embarks on solitary overseas vacations and indulges in practicing his shooting skills with the air rifle.
One fateful night, while watching the news, Nitram becomes fixated on a report about the Dunblane massacre. This ignites a dangerous obsession with firearms, prompting him to procure an illegal Colt AR-15 and shotgun, along with ordering a handgun. In a horrifying turn of events, he drives to the bed and breakfast his father had wished to buy and carries out a shooting spree against the new owners. His rampage continues at the café where the family had celebrated his birthday; after placing an order, he sets up a video camera, retrieves a rifle from his sports bag, and opens fire on unsuspecting tourists. Meanwhile, Nitram's mother, unaware of the unfolding chaos, nonchalantly smokes at home, oblivious to the news detailing the massacre playing in the background.
