When eight-year-old Oscar Madly discovers that his parents are getting a divorce, he withdraws into a vivid fantasy world brimming with joyful memories and chats with his talking pet hamster, Buffy. One fateful night, he witnesses a brutal homophobic assault on a teenage boy, culminating in the attackers driving a metal rod through their victim.

Fast forward ten years, and eighteen-year-old Oscar approaches graduation while setting his sights on a special effects make-up school in New York City. He takes a job at a hardware store to limit his time with his immature and homophobic father. At work, Oscar feels an unmistakable pull towards his new coworker, the charming and self-assured Wilder, yet he is deterred by a sharp, distressing pain in his stomach. At home, Buffy observes Oscar’s apparent happiness, hinting that he might be in love, a suggestion that he quickly brushes aside. Later, while inhaling the scent of a shirt he lent Wilder, Oscar attempts to pleasure himself but is abruptly interrupted by yet another wave of stomach pain.

As Oscar and Wilder’s friendship flourishes, his relationship with his father deteriorates further. When Wilder is dismissed from the hardware store and opts to relocate, he invites Oscar to a farewell costume party. Soon after returning home to prepare, Oscar receives heartbreaking news about being rejected from the only school he applied to. A confrontation erupts when his father catches him trying on some of his mother’s old clothes, leading to an explosive argument. In a moment of desperation, Oscar locks his dad in a closet and rushes off to the party. There, he spends the evening grappling with the uncertainty of Wilder’s sexuality, but the night takes a terrifying turn when he is assaulted by another guest named Andrew from Texas, plunging him into a series of haunting hallucinations. After losing consciousness, Oscar is revived by Wilder, who brings him to his treehouse. As they lie together, Wilder inquires about Oscar’s awareness of his sexuality. Initially evasive, Oscar ultimately confesses his confusion, and they share a long-awaited kiss.

Upon waking alone the next day, Oscar discovers that Wilder has vanished. To avoid confronting his father, he heads to his mother’s house, where he confronts her about leaving him during the divorce. She soothes him and proposes he move in with her. Realizing he left Buffy at his father’s place, Oscar rushes back, only to find that his belongings have been wrecked by his father, who refuses to reveal Buffy’s whereabouts. In the midst of a heated argument between his parents, Oscar scours for his beloved hamster, only to discover her lifeless body among his possessions. Overwhelmed by fury and a resurgence of stomach pain, he hallucinates a metal rod appearing from his own body. In a fit of rage, he extracts it and threatens his father.

Later at his mother’s house, Oscar reveals his rejection from the only college he had applied to. She encourages him to explore an artist’s colony on Fogo Island to channel his creativity. Upon arriving on the island, Oscar has a poignant final talk with Buffy, coming to terms with his true self. In a heart-wrenching revelation, Buffy admits that she is not the original hamster from Oscar’s childhood but rather a series of replacements orchestrated by his parents. Gently, Oscar places her in a small wooden boat and releases her into the sea, before returning to his room to reflect on the blissful memories he once shared with his father.