Greg Gaines embarks on a quest to narrate his chaotic senior year in high school, grappling with the perfect starting point for his story. He reflects on how, in a bizarre twist of fate, his failed film led to a tragedy that changed everything. This awkward, lanky teen, portrayed by Thomas Mann, navigates the halls of Pittsburgh's Schenley High School, straddling the various cliques that inhabit its complex social landscape. He shares friendly exchanges with the Jocks, the Stoners, and even the Theatre Dorks, maintaining a subtle yet pervasive presence among them all.
Despite not belonging to any one group, Greg finds comfort in his low-key connections, even mingling with the more marginalized groups like the goths. He often avoids the loud cafeteria scene, opting instead to have lunch in the office of Mr. McCarthy, his history teacher, portrayed by Jon Bernthal.
His world is shaken when he learns that his childhood friend, Rachel Kushner, played by Olivia Cooke, has been diagnosed with leukemia. Under pressure from his overprotective parents, Victor and Marla Gaines (played by Nick Offerman and Connie Britton), Greg attempts to reach out to Rachel, who initially refuses to meet him. However, after some persuasion, he finds himself at her home, where her mother, Denise (Molly Shannon), believes that he can be a supportive friend during this tough time.
During their first awkward meeting, they bond over an imaginative conversation about her pillow collection, which brings a flicker of joy to Rachel’s face as they share laughs over Greg's quirky storytelling. As their friendship blossoms, Greg introduces Rachel to Earl, his longtime collaborator and friend portrayed by RJ Cyler. Together, they create short films that parody popular movies, assigning ridiculous titles like "My Dinner with Andre the Giant" and "Pooping Tom." This creative outlet not only strengthens their friendship but also provides a welcome distraction for Rachel amidst her health struggles.
As Rachel undergoes chemotherapy, their bond grows deeper. Greg's ability to treat Rachel as more than her illness allows them to joke about her condition, forming an unexpected connection. He shares with her insights into his reservations about college, while Earl encourages him to showcase their film collection to Rachel, who finds great humor in their work, even as she faces the harsh realities of her treatment.
However, the situation takes a darker turn when Rachel decides to discontinue her chemotherapy after realizing it may be causing more harm than good. An emotional clash occurs between Greg and Rachel, revealing the cracks in their friendship as they navigate their fears and frustrations. Greg grapples with feelings of helplessness as he confronts Earl about their situation, and their friendship briefly frays.
In a bitter twist of fate, Greg learns that Rachel is moved to hospice care. Although initially invited to prom by his crush, Madison, he chooses to visit Rachel instead. When he arrives, he brings along a projection of the heartfelt film he made for her. This poignant moment begins happily but turns tragic when Rachel, watching the film in tears, slips into a coma and ultimately passes away.
As he faces the aftermath of her death, Greg reconciles with Earl and discovers a heartfelt note from Rachel, expressing her wishes for him to cherish her belongings and make something of his life. Feeling the profound weight of their shared memories, Greg resolves to honor Rachel by chronicling their story and sending it off to the college, complete with a warning that "the last person who saw this immediately went into a coma and DIED."
