Don, a 15-year-old struggling with the weight of his diagnosis—terminal cancer—finds himself lost in a world of comic stories that feature his own superhero. Ignoring the pleas of his therapist, he attempts to take his life by the train tracks but ultimately decides to let the train rush by without him. Haunted by hallucinations, he experiences a vision of a twisted woman laughing at him during a medical scan.
In a desperate attempt to intervene, his worried parents send him to therapy, where he meets psychiatrist Dr. Adrian King. Initially resistant, Don expresses his disdain for King's methods by leaving a graffiti mark, a Skull 'n' Crossbones, on the psychiatrist's boat. Eventually, he cleans it off and engages in a heartfelt conversation with King about his crush, Shelly.
During one of their encounters, Shelly improvises an essay, leaving Don in awe of her quick thinking. This sparks a connection between them as they exchange notes in class and make plans to attend a weekend party. This party serves as a turning point: Don and his friends concoct a recipe for a drink that blends wines and beers. Enjoying the high spirits, he catches sight of the hallucinated woman once more, leading him to graffiti her image on the school window, resulting in his suspension.
While trying to scrub off the graffiti, Shelly comes to assist him, deepening their budding friendship. Their relationship further blossoms during a rooftop conversation where Shelly shares her admiration for Don’s artwork, calling him talented and beautiful. However, the night at the party leads to embarrassment when a video of Shelly surfaces, sparking rumors and hurt feelings. When a peer mocks their relationship, Don, feeling cornered and defensive, denies their connection, which leads to Shelly storming off.
Back home, heartbroken and isolated, Don lashes out at King when he confronts him about his emotional state. This culminates in a panic attack, leading to a grim revelation at the hospital that his cancer has progressed, leaving him with only a few days to live. In a poignant moment, he shares a connection and a smoke with his father, who struggles with the harsh reality of Don's condition.
Throughout his hospital stay, Don bonds with a young cancer patient, exchanging dreams of the future, where she wishes to be a dancer, revealing Don's wish to become a superhero. Meanwhile, in a misguided but well-meaning attempt, Don's brother and friends seek to ensure that Don does not face his fate as a virgin, approaching several girls at school. This embarrassing endeavor eventually leads to a girl agreeing to meet him, but Don’s thoughts drift back to Shelly as he grapples with the idea of true love.
Haunted by a hallucination of the medic woman who once tormented him, Don realizes he must apologize to Shelly. He rushes to her, leading to a serene moment as they walk along the beach hand in hand. He makes her promise to visit the beach whenever she feels down, to remember him. Ultimately, Don passes away peacefully in his bed, leaving behind memories and connections that will linger in the hearts of those he touched.
Meanwhile, Dr. King boards his sailboat adorned with Don's signature skull design, while Shelly watches from a distance, reflecting on their meaningful but fleeting time together.
