Josh narrates a play-by play as he plays in a basketball game. He then introduces himself more fully: his name is Josh Bell, but people call him Filthy McNasty. He's tall, has long hair, and wants to be a basketball star. Josh got his nickname from one of Dad's favorite jazz artists, Horace Silver. When Josh expressed uninterest in Silver's work, Dad dedicated the next song, "Filthy McNasty," to Josh. At first Josh wasn't keen on the name, as others made fun of him for it. However, as he began to excel on the basketball court and as Dad praised him using that name, he started to like it. Josh also has a twin named Jordan who goes by the nickname JB. JB loves betting and Michael Jordan. Josh loves his locks more than anything. They differentiate him from JB, make him feel cool like his favorite rappers, and most importantly, Dad used to have them when he was a professional player. Dad's locks looked like wings. Sometimes, Josh asks Dad if he misses playing basketball and suggests that Dad could play again. Dad, however, insists that he's happy "coaching" the family. When Josh asks about Dad's championship ring, Dad tells Josh that when he becomes "Da Man," then he can wear the ring.
Right before a game, JB tries to dunk the ball. Josh laughs and, to show off, dunks. During halftime, JB asks to bet. The terms of his bet have many variables, but if JB wins, he wants to cut off one of Josh's locks. Josh initially declines, but then agrees, believing the bet is too specific for JB to win. His head starts to hurt as he watches every variable fall into place. After the game, the team cheers and chants as JB grabs Coach's scissors and starts to cut. Vondie yells, "OH SNAP," and Josh realizes something is wrong: JB cut five locks. Mom refers to this as a calamity and insists that Josh cut off the rest of his locks. The family goes out for dinner a week later. At the Chinese restaurant, Mom removes the salt from the table while JB grabs Josh duck sauce and wonton soup. Though Josh didn't say anything, JB knew exactly what food what Josh wanted.
Following his haircut, Josh mourns his locks. He eventually asks Mom for a box to put them in and she allows him to go into her and Dad's closet for a hatbox. Josh decides to open Dad's box of basketball memorabilia and JB joins him. The boys try on Dad's championship ring, flip through old articles, and then they find a folder containing two letters. One invites Dad to try out for the Los Angeles Lakers, while the other says that if Dad doesn't agree to surgery for patellar tendinitis, he won't play again. Josh wonders why Dad never got surgery.
At school, kids joke that they won't be able to tell Josh and JB apart now that their hair is similar. A new girl, whom Josh calls Miss Sweet Tea, asks the boys if twins know what each other are thinking. Josh tells her that, given the look on JB's face, a person doesn't need to be a twin to know what he's thinking. JB and Vondie discuss how beautiful Miss Sweet Tea is after she leaves. Josh, who's trying to do his vocabulary homework, refers to her as "pulchritudinous." He also wonders why Miss Sweet Tea is interested in JB. After dinner, Dad takes the boys to the rec center to practice shooting. They play a game with some local college guys who ask Dad for autographs and win the game. Dad takes them to Krispy Kreme after, insists that Mom doesn't have to know, and then tells the boys his favorite story of teaching them to play basketball. He tells them how, at three years old, the boys could shoot free throws like they were naturals.
After the next game, Miss Sweet Tea compliments Josh on his performance and then gives JB some sweet iced tea. Because Josh missed free throws during the game, Dad makes him shoot fifteen in a row when they get home. Mom rescues Josh from this exercise to read before bed. JB reads while listening to music, so he doesn't hear Mom and Dad's fight in the next room, but Josh does hear. Mom wants Dad to see the doctor for hypertension, but Dad refuses. Josh realizes that this is why Mom watches Dad's salt intake and thinks that his grandfather must've died of hypertension.
The week after Thanksgiving, JB asks Josh to pass Miss Sweet Tea a note for him during a test. The teacher catches Josh in the act and Josh chooses to take the fall for JB. At the office, Mom reprimands Josh and reminds him that he won't get into college if he cheats. Josh doesn't have the opportunity to explain himself. To make matters worse, gym class later is about CPR, not sports. Josh is forced to assist the teacher and jealously watches JB and Miss Sweet Tea pass notes.
Josh tries to talk to JB about basketball, but JB looks like he's barely listening. Josh knows he's too caught up thinking about Miss Sweet Tea. He takes his problem to Dad, but Dad just laughs and suggests that they get donuts. At the game later, Josh starts to refer to JB as a showoff. The team wins and later that evening, Mom calls Josh into the kitchen. She explains that they're going to have pita and hummus for dinner since Dad has hypertension and they need to eat better. Josh understands that this is important, but he feels victimized nonetheless. However, when Dad suggests he, Josh, and JB get barbecue after the next game, Josh lies that he's already eaten dinner. A few days later, Josh and JB are shooting free throws when Dad suddenly bends over. JB sprays him with the hose, which revives him, but Josh is worried. JB refuses to accept there's anything wrong, but Josh thinks he understands why Dad is afraid of hospitals: Dad's dad died there.
Miss Sweet Tea calls and asks for Jordan. Josh tries to give JB the phone, but JB runs away and asks Josh to speak for him. Josh is able to pull off the feat and successfully agrees on JB's behalf to be Miss Sweet Tea's boyfriend. JB is ecstatic. The next day at lunch, JB and Miss Sweet Tea walk up to Josh's table. JB calls Josh "Filthy," but suddenly, it seems like a dirty joke. At practice after school, Josh and JB have a strange experience where it seems like they both see a ghost at the same time, but they don't discuss it. JB hangs out with Miss Sweet Tea after school, so Josh goes to the library alone to do homework. He feels sorry for himself and to make matters worse, he discovers JB and Miss Sweet Tea kissing.
While Dad drives Josh to a basketball game, he gets pulled over. He doesn't have his license, so he and Josh are late to the game. Because Josh is late, Coach makes him sit out the first half. Rather than be a team player, however, Josh tries to act alone. When this doesn't work out, he throws the ball at JB so hard, he nearly breaks JB's nose. When Mom talks to Josh about his behavior later, Josh admits that he's afraid that JB doesn't love him anymore. Mom suspends him from the basketball team, so Josh spends the next week trying to make up for what he did. JB, however, ignores him. Josh watches games from the top of the bleachers with Mom and Dad and watches Dad yell at the ref. Inexplicably, Dad's nose starts to bleed after he yells. The next day, Mom threatens Dad if he doesn't go to the doctor. Not long after, the local paper names Josh their Most Valuable Player. Though most of Josh's classmates are happy for him, Miss Sweet Tea and JB aren't. JB continues to ignore Josh and finally, Josh writes a letter to his brother, explaining that he feels lost and alone now that they're not speaking. Josh feels even lonelier when Vondie gets a girlfriend too.
While Josh and Vondie are on the phone, Josh hears strange panting in his parents' room. He finds Dad there, cleaning up vomit and holding his chest. Dad brushes off Josh's concerns and shows him an offer of a coaching job. Josh is worried, but Dad insists that he and JB will be fine. During this conversation, Josh also asks Dad to call him "Josh," not "Filthy." Mom notices the look on Dad's face and looks panicked. They fight again and Dad continues to refuse to see the doctor. Soon after, Miss Sweet Tea comes for dinner. Josh decides to call her "the girl who stole my brother." She likes Mom's veggie lasagna and she also has a sister who attends Duke, the college Josh wants to attend. After dinner, Josh asks Mom if he can go with them to Dad's doctor's appointment the following week.
For the next game, Josh sits with the team and suddenly notices that Mom and Dad aren't in the bleachers. He and JB meet each other’s eyes and look like they've seen ghosts, but Mom texts Josh assuring him that things are fine. In the final week before the holiday break, Josh offers JB his list of vocabulary words to help him study, and JB thanks him for the help. At lunch the next day, Coach encourages Josh to make up with JB and shares that Mom will allow Josh to play in the championship game. Josh is ecstatic, but unsure how to make up with JB. He's not looking forward to the tournament he's supposed to be playing with Dad and JB, since he and JB are still feuding. However, the day before the tournament, JB starts to acknowledge Josh and laugh with him. Before the tournament, Josh and Dad play a warm-up game. Dad steals the ball from Josh's crossover and then collapses from a heart attack. Josh performs CPR.
The doctor tries to comfort Josh, JB, and Mom as he explains that Dad has a myocardial infarction and is in a coma. He encourages them to talk to Dad, but Josh is angry and doesn't want to talk when it's unclear if Dad can hear him. Josh tells Mom all the reasons he's angry, which include Dad's promise to be here forever, Miss Sweet Tea's existence, and his missing locks. Dad finally wakes up on Christmas Eve. After a Christmas spent in the hospital with relatives, Dad tells his sons that they need to always love and look out for each other. Then, he and Josh speak privately. Dad mostly refuses to answer Josh's questions; he wants to know if Josh is going to play in the championship game.
Just before the championship game, Mom gets the call that Dad had another heart attack and she leaves for the hospital. JB follows Mom on his bike, while Josh rides to the game with Vondie. In the last seconds of the game, Josh notices JB and Miss Sweet Tea sitting on the bench. JB is crying as Josh makes his final basket, winning the game.
Dad's obituary in the paper offers the highlights of his career and says he died at age 39. Josh feels unmoored at the funeral without any rules or basketball rituals. At home afterwards, Josh takes a phone call from Miss Sweet Tea. She apologizes and invites him to attend a college basketball game with her and JB. Then, Josh heads outside to shoot free throws. Soon, he's making them with his eyes closed. As he gets close to Dad's record of 50 in a row, he thinks he hears Dad's voice. It's actually JB. JB gives Josh Dad's championship ring and says that he must be Da Man now. Josh cries; he doesn't want the ring or the title. He gives the ball to JB to make the fiftieth free throw.