Starr Carter is a 16-year-old black girl who lives in the fictional, mostly poor black neighborhood of Garden Heights, but attends an affluent, predominantly white private school, Williamson Prep. After the police break up a party Starr is attending one weekend, Starr is driven home by her childhood best friend, Khalil. On the way home, they are stopped by a white police officer. The officer has Khalil, who is black, exit the car; while outside the car and talking with Starr, Khalil reaches back into the car for a hairbrush, which the officer mistakes for a gun. The officer shoots and kills Khalil.
Khalil's death becomes a major national news story. The media portrays Khalil as a gang banger and drug dealer, while more favorably portraying the white officer who killed him. Starr's identity as the witness is initially kept secret from just about everyone outside Starr's family, even her younger brother Sekani. This means that Starr's two best friends, Hailey Grant and Maya Yang, and Starr's white boyfriend, Chris, who all attend Williamson Prep together are unaware of Starr's connection to the news story. Having to keep this secret weighs on Starr, as does her need to keep her Williamson and Garden Heights personas separate. Starr's struggles with identity are further complicated when the family moves out of Garden Heights after her mother Lisa leaves her job as a nurse in a Garden Heights clinic for a high-paying hospital job.
Starr agrees to be interviewed by two detectives about the shooting after being encouraged by her Uncle Carlos, who is also a detective. Carlos was a father figure to Starr when her father, Maverick, spent three years in prison for gang activity. Following his release from prison, Maverick leaves the gang and becomes owner of the Garden Heights grocery store where Starr and her half-brother Seven work. Maverick was only allowed to leave the gang, the King Lords, because Maverick took the charge that saved the gang leader King from being locked up. King, widely feared in the neighborhood, now lives with Seven's mother and Seven's half-sister Kenya, who is friends with Starr.
After a grand jury fails to indict the white officer, Garden Heights erupts into both peaceful protests and riots. The failure of the criminal justice system to hold the officer accountable pushes Starr to take an increasingly public role, first giving an interview and then speaking out during the protests, which are met by police in riot gear. Her increasing identification with the people of Garden Heights causes tension with Starr's friends and especially with her boyfriend Chris. By the end of the novel, Starr and Maya have started standing up to Hailey's racist comments and Chris remains supportive of Starr.
The climax of the novel occurs during the riot following the grand jury results. Starr, Chris, Seven, and DeVante, a member of the King Lords who Maverick helps to escape by having DeVante live with Carlos, successfully defend Maverick's store from King. The neighborhood stands up to King and thanks to testimony by DeVante, King is arrested and expected to be imprisoned for a long time. Starr promises to keep Khalil's memory alive and to continue her advocacy against injustice.
