The film opens with Simon who, in a disoriented state, finds himself drooling over a lackluster meal while under the influence of a medication. After a curious worker inquires about his troubling side effects, Simon's gaze drifts to a nearby drooling girl who plays absentmindedly with her food, causing him to heave violently onto his plate. The scene shifts to Simon in a disheartening office where he faces disappointment regarding his compensation for participating in a drug trial, leading to a heated confrontation where he curses out the doctor.
He unexpectedly encounters the drooling girl again outside, and, noticing that it's Sunday with no bus available, he kindly walks her home. Dinner at her house soon takes a chaotic turn when her mother flirts with him in the kitchen, ultimately resulting in Simon inadvertently setting the family's bushes ablaze, making him a person of interest to the police.
Next, we are introduced to Patty, a socially awkward character who endures relentless bullying from jocks. Working at a pet store, she faces mockery, including having her sandwich stolen by the jocks, and returns home to a mundane family dinner where her requests to attend a concert are dismissed. She has an adopted brother, Kevin, who is unaware of his adoption status, leading to playful bickering. Later, in a moment of escapism, she indulges in her favorite punk band, Psyops, obsessively dancing and even daring to send a risqué photo to her idol, John Q.
Simon struggles to cash a check at a bank, confronts dealers for more drugs, and discovers an enigmatic black envelope addressed to "John Q. Public." A narrow escape from a police chase leads him to an alley where he finds Patty, who discreetly agrees to keep his location a secret. They bond over their shared past in a music appreciation class before Simon deceives her family by pretending to be a missionary in order to stay under their roof.
As their friendship deepens, Simon learns about Patty’s love for Psyops and her aspirations of attending their concert. When Patty reveals her affection for John Q, Simon realizes that the black envelopes in his bag are love letters she wrote to him, leading him to jump out of a window in frustration. The relationship becomes more complex as Simon entangles himself further in Patty’s life, even as he attempts to provoke vengeance against the jocks.
In a plot twist, Simon and Patty team up to retaliate against the bullies, humiliating them in a comical yet gratifying scene involving a dead cat and public shaming. Following a confrontation with Patty’s boss, they finally make progress in their romantic relationship, stealing moments together amidst the chaos of their lives.
As their bond grows, Simon eventually reveals his identity as John Q, showcasing how he treasures Patty's songwriting talent. Their intimate moments solidify their unity, but Simon's troubled past catches up with him when law enforcement intervenes at a concert, resulting in his arrest.
Despite the separation, Patty asserts her independence and strength by standing up to bullies, declaring herself as Simon’s girlfriend when questioned about their relationship. The film concludes with her embracing a new chapter; wearing Simon's ski mask, she confidently dances to their song, "Watermelon," signifying a promising evolution in her identity.
