Oliver Tate, played by Roberts, is a 15-year-old boy living in Swansea in 1986. He considers himself an unmatched genius, believing that he is adored by his peers, although in reality, he is quite the opposite—pretentious and socially isolated. His crush is on the outspoken and spirited girl named Jordana, portrayed by Paige, who brings a spark of excitement to his otherwise mundane life. To catch her attention, Oliver resorts to bullying an overweight classmate, convinced that such actions will earn him her admiration.
Their relationship takes an unexpected turn when Jordana invites Oliver for a secret meeting after school, requesting that he bring along a Polaroid camera and a diary. In a twist of teenage cunning, she captures moments of them kissing; however, this is all part of a scheme to make her ex-boyfriend jealous. Unfortunately, this plan backfires, leading to both Oliver and Jordana facing public ridicule. The situation escalates when Oliver is violently confronted for defending Jordana against derogatory comments. As they walk home, she takes his hand, leading to their first kiss, and they officially become a couple.
Back at home, Oliver becomes increasingly worried about the shaky relationship between his parents. His father, played by Taylor, seems to be battling depression, which only amplifies Oliver's anxieties. Compounding this situation is the arrival of Graham, portrayed by Considine, an ex-boyfriend of Oliver's mother Hawkins, who has a flirtatious demeanor that raises Oliver's suspicions about an affair.
As Oliver navigates his blossoming relationship with Jordana, he learns that her mother is suffering from a potentially deadly brain tumor. In a misguided effort to spare Jordana further heartache, Oliver even contemplates poisoning her beloved dog. Their relationship is tested further when Oliver attends an early Christmas dinner with Jordana’s family, witnessing her father’s emotional breakdown, which unsettles him and prompts him to abruptly cut ties with Jordana, believing it to be in her best interest—a demonstration of his unintended harshness.
Fueled by fears that his mother and Graham are having an affair and seeing his father in a despondent state, Oliver tries desperately to mend his parents' relationship. One night, after discovering his mother and Graham have gone to the beach, he attempts to track them down. In the process, he spots Jordana with a new boyfriend, which shatters him. In a fit of rage and heartbreak, he breaks into Graham’s home, where he ends up getting drunk and engaging in minor vandalism. When Graham finds Oliver, he surprisingly returns him home with little fuss.
The following morning, Oliver is relieved to see his parents are not angry and appear to be reconciling, despite his mother’s cryptic admission about an intimate incident with Graham. Yet, Oliver’s heartache over Jordana remains unresolved, and he is unable to reach out to her to explain his erratic behavior. Weeks pass as he sulks in his misery, until he unexpectedly spots her on the beach. He rushes towards her to apologize, only to discover that she has ended her relationship with her new boyfriend. The future of their relationship remains uncertain, leaving viewers to ponder whether this young couple will find their way back to each other.
