Seventeen-year-old Ben Marshall is navigating the tumultuous waters of adolescence in a household shaped by the contrasting personalities of his parents. His father, Robert, is a complacent vicar fixated on ornithology, while his domineering mother, Laura, seems more interested in her charitable endeavors than the emotional well-being of her family. She imposes unrealistic demands on Ben, such as making him deliver meals on wheels, all while she juggles an affair with Peter, a young curate playing Jesus Christ in the church pageant she directs, despite her strong Christian values.
Laura’s overbearing nature extends to prohibiting Ben from having a mobile phone or spending time with peers. Instead, she uses Ben's driving lessons as an opportunity to pursue her illicit relationship with Peter. This leaves Ben feeling isolated and unhappy, prompting him to express his feelings through poetry directed at Sarah, a girl he knows from church. However, when he shares his latest creation, the "Sarah Poem," he faces rejection.
Under pressure from his mother, Ben searches for summer work to help support Mr. Fincham, a mental patient adopted by Laura. He responds to a job advertisement placed by Dame Evie Walton, an alcoholic actress whose career has waned. Evie, in need of companionship and assistance, quickly forms a bond with Ben and offers him a job.
When Laura denies Ben the chance to join Evie on a camping trip, the two settle for a drive in the countryside. During their excursion, Evie cleverly hides the car key after they find a picturesque camping spot. The next morning, she insists they attend the Edinburgh International Book Festival, where she has been invited to read poetry. This road trip becomes a pivotal moment for Ben, marking his first sexual experience with Bryony, a young woman at the festival. Through these experiences, Ben gains insight into the importance of responsibility and discovers the strength to assert himself.
Upon returning home, Ben faces interrogation from Laura, who is convinced that Evie has negatively influenced him. Following a failed visit from Evie, Ben shocks himself by walking offstage during the pageant and cycling to Evie's residence, where the two reconcile their friendship.
Evie returns to the pageant, playing the role of God and inciting fervor among the crowd. This prompts Ben to join her in a moment of freedom, but Laura pursues them, wielding the Bible in a desperate attempt to regain control. In a twist of fate, Laura gets run over by Mr. Fincham, whose mental health continues to deteriorate. During a hospital visit, Laura claims that a near-death experience has granted her prophetic insight, stating that God demands she leave Robert and run away with Peter, who has been dismissed by the Bishop.
Ben, overwhelmed, confronts Sarah about the affair, expressing his frustration when she trivializes it as God's will. Following Evie’s advice, he purchases a tent and sets up camp in the backyard, rejecting the toxic influence of his mother. When Robert approaches him, Ben lashes out, insisting it is his father's turn to initiate a divorce, to which Robert reveals that he has long wanted to leave but has remained faithful out of love.
With Laura's oppressive influence finally behind him, Ben reconciles with his father. He later visits Evie to share his plans to move to Edinburgh for university studies in English. Although Evie is happy for him, she feels the sadness of losing Ben as a helper. In a gesture of gratitude, Ben reads her a final poem, to which she responds warmly. As the film concludes, Ben strides through a park, finally liberated and ready to prepare for his new chapter in Edinburgh.
