Set in 1940s Chicago, the story follows Clemson "Clem" Thurber Jr., a young Black boy whose life is upended when his father is killed in the Port Chicago Disaster, a catastrophic explosion at a naval base near San Francisco. One night, when Clem is nine, two white soldiers knock on the family's door to deliver the news. Clem's mother, Cecille, screams and collapses. His oldest sister, Clarisse, 14, takes charge while his other sister, Annette, 13, fetches water. Momma enters a near-catatonic state for days. Her sisters, Aunt Dorcas and Aunt Bethel, arrive from Washington, DC, and gradually coax her back to functioning. At a memorial service, photographs of Clem's father stand on the pulpit in place of a casket; when soldiers present a folded flag, Clarisse accepts it because Momma cannot reach for it.
Clem has few memories of his father, who left for the navy when Clem was five. His clearest is of a day near the Ashley River in South Carolina, where his father carried him on his shoulders into the water. One morning, Clem spins a fantasy about Momma going undercover as a spy-cook who poisons enemies with her eggs. Momma shakes, and Clem fears he has upset her, but she turns around laughing for the first time since the soldiers came. Clem resolves that if he tries hard enough, he can still make her laugh.
At Lincoln Elementary, Clem is small for his age but so academically gifted that he is skipped from third to fourth grade after being caught whispering answers to classmates during tests. The older students mock his size but rely on him, earning him the nickname "Professor." With Daddy's navy pay gone, Momma applies for secretary positions at white office buildings but is rejected despite being well qualified. Eventually she takes a job she does not want: working as a maid for the Franklin family, a white household in Hyde Park. On her first morning, she cries at the ironing board pressing a gray uniform before Clarisse takes the iron from her hand.
With Momma working long hours, Clarisse takes on a maternal role and Annette keeps the apartment spotless, while Clem is told to focus on schoolwork, leaving him feeling useless and excluded. He forms a reluctant friendship with Errol Watkins, a near-silent boy who moves in downstairs. Their mothers, both maids in Hyde Park, insist the boys walk to school together. Clem eventually realizes that Errol's father is hurting Mrs. Watkins.
Every summer in DC, the aunts fill the children's days with history lessons and monument visits. The children also visit Uncle Kent, Daddy's older brother, in Milwaukee, where Clem bonds with his cousin Kendrick, who gives him a pocketknife. Uncle Kent tells Clem that Clemson Sr. loved the water and was "just good folk." When the family returns to Chicago, fireworks erupt across the South Side as the war ends. Momma breaks down on the front stoop, crying for the husband she will never welcome home.
In sixth grade, Lymon Caldwell arrives at Lincoln Elementary. Small but fearless, Lymon punches the school bully, and the three boys become inseparable as the "Three Musketeers." Clem notices Lymon frequently arrives at school looking beaten up and understands he is being abused at home. Momma also arranges swim lessons for Clem at a white pool through the Franklins. At the first lesson, the thought of his father blown apart at the bottom of the Pacific overwhelms Clem and he vomits. He fakes illness to avoid further sessions. That summer in DC, a patient instructor at an all-Black pool works with Clem one-on-one, but all he manages is dipping his face in and out of the water.
In seventh grade, Langston, a large, quiet boy from Alabama, arrives and is nicknamed "Country Boy." Lymon mocks his accent and shoves him; Clem participates reluctantly, laughing along even as guilt churns his stomach. At the library, Clem discovers Langston shares his love of reading. The bullying worsens Clem's stomach problems, and time alone forces him to confront his shame: Nothing about beating on someone who will not fight back makes him "good folk." The breaking point comes when Lymon rips pages from Langston's library book of Langston Hughes poetry. Langston fights back, twisting Lymon's arm behind his back. Clem runs for a teacher, then collects the scattered pages. During Lymon's suspension, Clem bonds with Langston over shared loss, as Langston's mother also died. When Lymon returns, Clem refuses to participate and breaks from both Lymon and Errol. Lymon is later sent to juvenile detention. When Momma offers to intervene, Clem tells her some things he can fix himself.
One afternoon at DuSable High School, Clem discovers the pool and watches the swim team practice, mesmerized. At a swim meet, he meets Anthony, a swimmer and lifeguard who has a crush on Annette. Clem admits he is afraid to swim. Anthony offers to teach Clem if Clem puts in a good word with Annette. After giving one lesson, Anthony secures permission from Coach Palmer for regular sessions. Slowly, Clem learns to swim without support. After getting home late from an early lesson, he confesses everything to Momma, who tells him his father would be proud. When Clem asks if he is like his daddy, Momma says he is funny and kindhearted like his father and that his father loved maps too, before growing too emotional to continue. For the final lesson, Anthony arranges a surprise: Annette, Clarisse, and Momma come to watch. Clem swims 25 yards, the full length of the pool including the deep end, for the first time. He does not win his race against Anthony, but when he touches the wall, everyone claps.
At home, tensions erupt when Momma raises the subject of Clarisse attending Howard University. Clarisse lashes out about the family's finances and spits the word "maid," throwing Momma's job in her face. Momma slaps her. When Momma raises her hand again, Clem grabs her arm and says, "Stop." Clarisse breaks down sobbing that Daddy is gone and never coming back, and Momma wraps her arms around her. Annette later shares memories Clem does not have: Daddy calling his daughters "my angels," dancing with Momma. She tells Clem that when Momma looks at him, she sees Daddy. Clem cannot miss his father the way the others do, because he never knew him long enough, but he recognizes the family's shared grief.
When Anthony mentions he gave up his
Chicago Defender newspaper route, Clem asks to take it over. His family resists, but Clem insists he is only treated like a baby because they will not let him be anything else. Each morning he rises before Momma, uses Kendrick's pocketknife to cut the twine on his paper bundles, and delivers papers before school. He gives his first pay to Momma. Reading the
Defender sparks a dream of becoming a reporter rather than joining the navy. On his early-morning route, in the pre-dawn stillness, Clem realizes he is no longer wondering whether his father would be proud of him. For the first time, he is proud of himself. He concludes he is Clemson Thurber Junior: not half his daddy but part his father, part his mother, and mostly himself.