Fourteen-year-old Junior, also known as Arnold Spirit Jr., lives on the Spokane Indian Reservation in Washington. Born with hydrocephalus, he has a stutter and seizures, making him an easy target for bullies. He finds solace in drawing cartoons, dreaming of escaping the reservation's poverty and hopelessness.
Junior's best friend is Rowdy, who shares his rebellious spirit. Both long for better lives. When Junior discovers a prestigious white high school nearby, Reardan, he sees a chance to change his destiny. The idea is met with resistance from Rowdy, his family, and the entire reservation. Junior, however, feels stifled and determined to pursue his education.
Leaving behind his family and community, Junior starts his freshman year at Reardan. He's the only Native American student, feeling awkward and isolated. The wealthy white students treat him with indifference or hostility, calling him names and making racist jokes. He yearns for acceptance but struggles to fit in.
Despite the challenges, Junior excels academically. He finds friendship with Penelope, a quirky and supportive classmate who appreciates his drawings and encourages his artistic talent. However, Junior often feels torn between his two worlds. At Reardan, he strives to succeed but misses the familiar traditions and warmth of his reservation home.
Back on the reservation, life is tough. Junior's alcoholic parents struggle to make ends meet. His sister, Mary, withdraws from the world, haunted by trauma. Witnessing their hardships weighs heavily on Junior, creating a constant internal conflict.
Life takes a tragic turn when Junior's best friend, Rowdy, commits suicide. Junior is devastated, but he seeks solace in his art, pouring his emotions and experiences into his cartoons. He creates a comic strip called "The Absolutely True Diary of a Part-time Indian", reflecting his life straddling two worlds. His art gains recognition, showcasing his perspective and talent, and even wins him an award.
Despite the award, Junior still feels like an outsider in both communities. At Reardan, he clashes with his white teachers and classmates over their ignorance and stereotypes about Native Americans. On the reservation, he faces accusations of betrayal and assimilation.
Junior finally finds a mentor in Mr. P, a history teacher who understands his struggles and encourages him to embrace both his Native American heritage and his desire for education. With Mr. P's support, Junior learns to stand up for himself and his culture, using his voice to challenge prejudices and stereotypes.
As the year progresses, Junior begins to find his place. He maintains his connection to his family and community while thriving academically at Reardan. He still experiences challenges and conflicts, but he learns to navigate them with greater confidence and strength.
Junior leaves for an out-of-state basketball tournament with his Reardan team. He looks back at the reservation, feeling a bittersweet mixture of sadness and hope. He understands that his journey is far from over, but he's now armed with the knowledge and courage to embrace his unique identity and pursue his dreams, bridging the gap between his two worlds.