Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Initial Situation
Arnold is the reservation outcast.
Arnold Spirit, Jr. is a teenage boy with a pretty tough life. First of all, he lives in poverty on a Spokane Indian Reservation and is the son of two alcoholics. He's also a hydrocephalic, which means he was born with "water on the brain" and is susceptible to seizures. This makes him the reservation weirdo, and he's regularly beaten up and picked on by almost everyone. (His sole defender is his best friend, a tough-guy named Rowdy.)
Arnold is hilarious and talented, and draws cartoons for his amusement and ours. He hates living in poverty and dreams of something better for himself, maybe as an important artist. Arnold is presented as someone who is deeply dissatisfied with his situation in life. He's impoverished and abused by bullies and hopes his life will change—but, for the moment, there's not much he can do. (Or so he thinks.)
Conflict
Arnold fights back.
One day in geometry class, Arnold finds his mother's name written in the front of his geometry book. This means that his school is so poor that they've been using the same textbooks for at least thirty years.
Absolutely infuriated with the school's lack of resources, Arnold decides to fight back the only way he knows how. He throws the geometry book at his teacher, Mr. P. Arnold is later visited by the geometry teacher (now with a broken nose) who tells Arnold that he must leave the reservation. Mr. P says that everyone else has given up—but that Arnold is a fighter and cannot ever give up. He must go somewhere else—somewhere where people have hope.
Complication
Arnold leaves the reservation—and becomes a part-time Indian.
Arnold decides that, in order to get a decent education, he must transfer to the privileged white school twenty-two miles away in the town of Reardan. His parents agree, but not everyone on the reservations reacts so kindly. His best friend Rowdy hauls off and punches him in the face. The rest of the reservation begins to shun him as well, and treat him as a traitor to his people.
At Reardan, Arnold has some trouble fitting in, though he attempts to woo Penelope, the lovely blonde girl, and befriends Gordy, the school's resident genius. He also punches the school jock, Roger, in the face—and wins his respect.
The push and pull between Reardan and the reservation make Arnold feel like a part-time Indian. Having a bit of an identity crisis, he tries to figure out just who he is. Can he reconcile Junior (of the reservation) with Arnold (of Reardan)? Does he always have to have a split personality?
Climax
Arnold plays basketball against his old high school team—and loses. And wins?
Inspired to dream big, Arnold joins the Reardan basketball team and makes varsity. In the first match against his old school, the entire crowd from the Spokane Reservation turns their back on him. (Ouch.) Then he's pelted in the head with a quarter by someone in the stands, and then Rowdy knocks him unconscious with an elbow to the head. His team loses. In the rematch, though, Arnold starts the game with a star play, and it's a cakewalk from there. Reardan destroys the team from Wellpinit.
Though he's carried by his team on their shoulders, Arnold feels torn in two, as the team he beat used to be his own. The win against Wellpinit is tinged with disappointment, as Arnold realizes that he's been playing on the side of Goliath—not David. Is that who he really is?
Suspense
Arnold experiences a series of devastating losses.
Arnold loses a whole bunch of people who are very close to him: his grandmother is hit by a drunk driver, his father's best friend Eugene is killed in an accidental shooting, and his sister dies in a trailer fire. Confronted with a whole heck of a lot of suffering, Arnold has to learn how to carry on in the face of such pain, much of it totally senseless and preventable.
During this time, the reservation stops their silent treatment of Arnold and rallies around him and his family during his grandmother's funeral. In order to cope with the senselessness of it all, Arnold learns to embrace life. He makes lists of his favorite books, foods, and bands. He thinks about all of the things that make him happy and bring him joy.
Denouement
Arnold accepts his himself.
Arnold and his family visit the graves of Eugene, Grandmother Spirit, and Mary. He cries for his people and himself and his loneliness. He has kind of an epiphany, though. He realizes that he really doesn't have to see himself as a person split in two. He sees that he is a part of many different tribes (he is not only an Indian, but a cartoonist, and a son, and a basketball player, and a bookworm, and so forth). Arnold knows that he is not from Wellpinit or Reardan, but that he is a multi-dimensional person. Arnold becomes multi-tribal.
Conclusion
Arnold and Rowdy reconcile.
Over the summer, Rowdy asks Arnold to play a game of one-on-one basketball. Rowdy has begun to understand and accept Arnold's choice to leave the reservation. He tells Arnold about some old-time Indians he read about and how they used to be nomadic—meaning they moved from one place to another. He thinks Arnold is very much like these nomads.
Rowdy tells Arnold about a dream that he had in which Arnold was standing on the Great Wall of China. Rowdy tells Arnold that in the dream he was happy for him. Arnold cries. Not only has Arnold come to terms with who he is, but Rowdy is also trying to see and understand Arnold's new sense of self.