Bud, Not Buddy is the story of a ten-year-old African American boy named Bud Caldwell and his quest to find his father during the Great Depression. The novel begins in Flint, Michigan, at “the Home,” where Bud and other orphaned children wait to be placed into foster care. This will be Bud’s third foster family. His mother has died, and he believes that a flier she kept for a jazz band featuring a bass player named Herman E. Calloway is a clue to finding the father he never knew. He keeps the flier in his suitcase along with his other prized possessions. Apart from this flier, the most important thing Bud has is his mental list of life lessons, which he calls Bud Caldwell’s Rules and Things for Having a Funner Life and Making a Better Liar Out of Yourself.

Bud is unsurprised when Todd, the older boy at his new home, beats him up. Todd’s mother, Mrs. Amos, blames Bud for the fight and threatens to send him back to the Home, which sounds just fine to Bud. Mr. Amos then locks Bud in the family’s shed. In the middle of the night, Bud believes he sees a vampire bat Todd warned him about hanging from the ceiling. He takes a swing at it with a rake, but the bat turns out to be a hornets’ nest. After being stung multiple times, Bud escapes through the window. Then he sneaks back into the house, retrieves his suitcase, and enacts his revenge on Todd by pouring warm water on the older boy’s pajama pants, causing Todd to wet the bed. Todd had previously told Bud that his mother hates bed-wetters.

Now “on the lam,” Bud decides to seek help from Miss Hill, a librarian. He spends the rest of the night under a tree outside the library. Before sleeping, he takes stock of the items in his suitcase: the flier, a blanket, a collection of rocks, and a picture of his mother. Bud remembers his mother telling him that his name is not Buddy but Bud, like a flower waiting to open, and that when one door closes, another opens. There were many other things Bud’s mother told him she would explain to him one day, but now that she is gone, Bud supposes he will never have all the answers to his questions.

The next morning, Bud arrives late to the mission where free breakfast is served, but a couple beckon him over to join their family, pretending Bud is their son. They all eat breakfast together before Bud heads back to the library. When he gets there, however, the librarian on duty tells Bud that Miss Hill has married and moved to Chicago. Bud is deeply disappointed. Resolved not to return to the overcrowded Home, he returns to the tree to sleep.

Bud is awakened by the arrival of his friend Bugs, who has run away from the Home to “ride the rails,” or hitch rides on train cars. Bud agrees to come with him. When they ask at the mission about catching a train, the boys are directed to a nearby town called Hooverville, which they find by following the railroad tracks. Hooverville turns out to be one of many makeshift camps all across the country—and all named after President Hoover—where people stop to rest before hopping the next train. Bud and Bugs are welcomed and given food by a large group of people around a fire. Afterward, as the boys wash dishes in the river, Bud meets a girl named Deza Malone with whom he shares his first kiss. Deza tells Bud he is too young and innocent to ride the rails, and Bud himself has some doubts about the plan. In the morning, the train starts to leave early. Police try to prevent people from boarding, and the boys have to run. Bugs boards the train, but Bud is unable to catch up after pausing to retrieve his flier when it flies off his suitcase. More police then arrive to destroy Hooverville.

Bud returns to Flint, where he eats breakfast at the mission before returning to his tree. When the library opens, he borrows an atlas and calculates that it will take him a day and a night to walk to Grand Rapids, where he believes Herman E. Calloway lives. Bud is convinced that the jazz musician is his father. He spends the rest of the day reading in the library, then sits under his tree to eat a sandwich the librarian gave him and contemplate the contents of his suitcase.

Bud starts walking along the road to Grand Rapids at nightfall. Around two-thirty in the morning, a car pulls over. The driver beckons to Bud and eventually gets him to come out of hiding with the promise of food. He explains that he is concerned about Bud’s safety, as it isn’t safe for a young African American boy to be walking alone at night in this especially racist area. Bud accepts a ride to Grand Rapids by way of Flint but is terrified when he sees the man move a box of blood to the back of the car. Convinced the man is a vampire, Bud gets into the driver’s seat and speeds away, but the car dies. The driver catches up with him, introduces himself as Lefty Lewis, and explains that he is delivering the blood to the hospital in Flint. Bud relinquishes the car, enjoys the sandwich and soda Lefty gives him, and falls asleep in the passenger seat. When he wakes up, he finds himself in the home of Lefty’s daughter, Mrs. Sleet, and her two children. The happy family share their breakfast with Bud before he and Lefty leave for Grand Rapids.

On the drive, Lefty tells Bud that he has wired Herman E. Calloway to tell him his son is safe, which makes Bud nervous. It is even more nerve-racking when the two are pulled over by the police, who explain that they are looking for labor organizers. Once the police leave, Lefty reveals that while he isn’t a labor organizer himself, he is delivering fliers promoting a strike. He tells Bud about labor unions, and a little while later, Bud falls asleep. When he wakes up, they have arrived at the Log Cabin, a Grand Rapids nightclub advertising Herman E. Calloway and his band, the Nubian Knights of the New Deal.

Bud goes through the first set of doors into the club, waits, then comes back out and tells Lefty he has made sure his father is inside, after which the two say their goodbyes. Bud then actually enters the club and sees the six members of the band putting away their instruments. When the man Bud thinks must be Herman E. Calloway turns around, however, Bud is surprised to see that the man is old. Nevertheless, he boldly announces that Herman is his father. Herman, gruff and unconvinced, wants nothing to do with Bud, but Jimmy, the trumpet player, realizes this must be the boy from the telegram. He makes a deal with Bud: he will feed him as long as Bud answers his questions honestly. After Bud helps the band pack up their instruments, they take him to a restaurant called the Sweet Pea run out of a woman’s living room. Bud sits at a table with Jimmy, Herman, and the band’s beautiful vocalist, Miss Thomas, who reacts with compassion and concern to Bud’s hornet stings and experience with the Amos family. Herman continues to act uninterested and goes to sit with the rest of the band while Miss Thomas gently tries to dissuade Bud from the notion that Herman is his father. Bud enjoys a delicious meal and the company of the band in spite of Herman’s grouchiness, feeling for the first time like he is where he belongs. Suddenly, he finds himself crying—something he thought he had forgotten how to do. Miss Thomas comforts him, and Bud feels like he has come home.

Miss Thomas takes Bud to Grand Calloway Station, the house where the band members live and where Bud will be sleeping that night. She shows him to a bedroom that looks as though it once belonged to a little girl. When Bud expresses concern that the girl will be unhappy to find him there when she comes back, the vocalist replies that he doesn’t have to worry about that. A short while later he hears Miss Thomas and Herman arguing in the hallway. Herman comes in to lock the closet doors, telling Bud that he is going to send him back where he belongs and that the boy had better refrain from “snooping.” Bud decides Herman is too mean to be a father to anyone, but as he falls asleep on the comfortable bed, he thinks of his mother and feels completely safe.

The next day, Bud overhears Miss Thomas and Herman in the kitchen debating what to do with him. Bud pretends not to have heard. When he enters the kitchen, the band members tease Bud for having slept in past noon, and Miss Thomas tells him that although they will have to ask some questions in Flint, they want Bud to stay with them and be part of their family. He will be expected to take care of chores and practice music two hours a day just like the rest of the band. Steady Eddie, the saxophonist, gives Bud a saxophone case to replace his old suitcase and a recorder to learn to play. The band members also give him a new nickname: “Sleepy LaBone.” Bud is overwhelmed with happiness and gratitude.

Herman tries to break Bud down with a regimen of tough chores, but Bud is used to hard work and has fun mopping the floor in the band’s practice space. When the Nubian Knights start rehearsing, Bud is mesmerized by the music, especially by Miss Thomas’s voice and Steady Eddie’s saxophone. After he has been living at Grand Calloway Station for about a week, Bud takes his third road trip with the band. After the show, he is unhappy to learn he will be riding with Herman, who makes Bud pick up a rock for him outside the club. When Herman puts the rock in his glove box, Bud is surprised to see a whole collection of rocks with dates and names of cities on them—just like the rocks Bud has carried with him for years. When they pull up in front of Grand Calloway Station, Bud shows Herman his rocks and the bandleader accuses Bud of stealing. Jimmy asks Bud where his rocks came from and Bud replies that they belonged to his mother, Angela Janet Caldwell. Herman walks into the house in a daze and locks himself in his room. Jimmy explains that Angela Janet was Herman’s daughter’s name, meaning the bandleader is probably Bud’s grandfather.

In the kitchen, Miss Thomas and Jimmy question Bud about his mother. He runs up to his room to get a photograph of her to show them and discovers Herman there, sobbing. Bud finds the photograph and pats Herman on the back. Downstairs, Jimmy and Miss Thomas confirm that Bud’s photograph is of Herman’s daughter, and Bud realizes that the room he has been staying in once belonged to his mother. Miss Thomas tells Bud that Herman had loved his daughter but had pushed her too hard to be successful, prompting Angela to run off with one of the band’s former members. She also gives Bud a picture of Angela as a teenager and explains that Herman brought his daughter a rock from every gig the band played from the time she was a little girl.

Miss Thomas and Jimmy leave to check on Herman, and the rest of the band come in with a gift for Bud: his very own saxophone. Steady Eddie promises to give Bud his first lesson after Bud has polished his instrument. Excited and grateful, Bud goes upstairs, where he hears Herman and Miss Thomas talking in Miss Thomas’s room but doesn’t stop to listen. He leaves his collection of fliers and all his rocks but one on his grandfather’s dressing table. Then he puts his photograph of his mother up on the wall of her old room and plays his saxophone for the first time.