In the picturesque Yorkshire countryside, a seemingly chance encounter unfolds when Mona, who is sprawled in a field, draws the attention of Tamsin, a girl from a wealthy lineage riding by on horseback. Recently suspended from boarding school, Tamsin appears disillusioned with her privileged life, much like Mona, who comes from a working-class background and is solely accompanied by her brother, Phil.
As Mona navigates her complex feelings, she witnesses Phil purging their late mother's pub of alcohol after his release from prison. Since his imprisonment for minor crimes, Phil has embraced religion, transforming the pub into a gathering place for local Christians. Amidst her struggles, Mona meets her lover, Ricky, for a brief rendezvous, only to be left heartbroken when he breaks off their relationship shortly after.
As they spend the next day together, Mona and Tamsin indulge in a carefree mix of drinking and smoking while confiding in each other about their dissatisfaction with life. Tamsin leads Mona to a location she claims is home to her father's mistress, where Mona's rebellious spirit emerges as she vandalizes her father's car, prompting a hasty retreat. In a gesture of friendship, Tamsin surprises Mona with an engine for her scooter, which leads the girls to a secluded river, where they share a moment of intimacy under a cascading waterfall.
Their adventures continue at Tamsin's home, where they explore her wardrobe and delve into Tamsin's past, marked by the tragic loss of her sister, Sadie, to anorexia. In a moment of blissful escape, they dance together in the garden as Tamsin, with an ethereal touch, plays the cello. Their connection deepens through passionate kisses and eventual intimacy, although they are interrupted by Phil, who seeks Mona for a community ceremony.
As the storyline progresses, Tamsin's intrigue with Phil surfaces, adding complexity to their triangle. Their bond only intensifies when they discover a stash of magic mushrooms, leading to a wild night out that disturbs the peace of the local dance hall. Declaring undying love, they engage in a dramatic suicide pact, cementing their deep emotional ties.
Phil's invasive presence leads to a series of confrontations, including a troubling incident where he chokes Tamsin after her mock seduction. In a fit of rage mixed with vulnerability, Phil attempts to control Mona, leading to a shocking display as she fakes a suicide attempt during a Christian meeting, which spirals into chaos.
Determined to leave, Mona packs a suitcase, but upon reaching Tamsin's house, she discovers the painful truth: Tamsin is returning to her privileged school, and her sister Sadie is still alive. Heartbroken and feeling betrayed, Mona goes to the river where she and Tamsin share a fleeting moment of connection. Tamsin quietly criticizes Mona's naivety, prompting Mona to lead her into the water for one final kiss, where the tension culminates as she momentarily takes Tamsin under, before finally releasing her and walking away, leaving their fateful bond uncertain.
