Part 1 alternates between the narrative and the letters Justyce McAllister, a black seventeen-year-old boy living in Atlanta, writes to Dr. Martin Luther King Jr.—to whom he refers simply as “Martin”—in which he reflects on his life and explains how he tries to live more like Dr. King.
In the middle of the night, Justyce goes to rescue his ex-girlfriend, Melo Taylor, from driving home drunk. When the police arrive, Officer Castillo misreads the situation and puts Justyce in handcuffs using excessive force. Justyce is finally released with the help of Mrs. Friedman, a lawyer and the mother of his friend, Sarah-Jane, or SJ. In a Dear Martin letter, Justyce talks about being from a rough neighborhood, attending Braselton Preparatory Academy on full scholarship, and having plans to attend an Ivy League college.
The brutal treatment he received from the police reminds Justyce of the recent police shooting of a black seventeen-year-old with a promising future. Hanging out with his best friend Manny Rivers, a wealthy, black Braselton Prep student, the two talk about Justyce’s on-and-off relationship with Melo. Over dinner, they learn that Manny’s cousin, Quan Banks, a gang member from Justyce’s neighborhood, has killed Officer Castillo. In class, Justyce, SJ, and Manny’s friend, Jared Christensen, both of whom are white, debate with their teacher and debate coach Dr. Jarius “Doc” Dray whether racial equality exists in America. Jared claims America is now color-blind.
On the weekend, Justyce goes to a Halloween party with Manny’s friends Jared, Kyle, and Blake. Jared suggests the boys dress as stereotypes. Justyce dresses as a thug and Blake as a Klansman. At the party, one of the Black Jihad, a gang from Justyce’s old neighborhood, punches Blake for his offensive costume and criticizes Manny and Justyce for hanging out with these white boys. Later, SJ and Justyce have a late-night conversation during which Justyce realizes how much he likes SJ. The next day, SJ celebrates Justyce’s acceptance at Yale University. In Doc’s class, Jared complains about affirmative action, claiming that an undeserving black student may have taken his spot at Yale. Later, Manny observes that SJ seems perfect for Justyce, but Justyce says his mother doesn’t want him to date a white girl. Manny confesses to being afraid of black girls because of his lack of exposure to them.
Some weeks later, Justyce and SJ win their debate tournament about racial profiling. Justyce then tries to kiss SJ, but she turns away. Confused, Justyce gets even more upset when he finds out that another black teen has been killed by the police. In reaction to these events, Justyce gets drunk and goes with Manny to Blake’s birthday party. Angered by their displays of racism, Justyce hits Blake and Jared. Justyce worries whites will only ever see his skin color and thinks his experiment to be like Martin Luther King Jr. has failed.
Later, Doc visits a hungover Justyce in his dorm room. Justyce tells Doc about his alcoholic, abusive father, whom he doesn’t want to be like. Doc encourages Justyce to hold on to his value despite other people’s racism. A couple days later in Justyce’s dorm room, Manny says his eyes are now open to racism. He tells Justyce he has quit the basketball team and that he has hit Jared for a racist comment that Jared made.
Later, Manny’s dad talks to the boys about the racism he experiences at work and his regret that he hadn’t better prepared Manny for racism. The next weekend, because Manny feels upset by Jared’s dad pressing assault charges against him, he and Justyce drive around, playing music loudly. Manny has an angry exchange about his music volume with a white driver, who turns out to be an off-duty police officer, Garrett Tison. The officer shouts a racial slur and fires three shots that injure Justyce and kill Manny.
In part 2, the narrative is interwoven with news reports. Disillusioned, Justyce stops writing his Dear Martin letters. After being released from the hospital, Justyce attends Manny’s funeral and reconnects with SJ. Newspaper articles follow the Tison case and report that Tison will stand trial for shooting Justyce and Manny. Justyce receives a free car. Manny’s parents give Justyce an heirloom watch in memory of Manny and tell him that Manny’s cousin Quan wants Justyce to visit him in juvenile detention. During Justyce’s visit, Quan explains the Black Man’s Curse and encourages Justyce to seek support from the Black Jihad. The media misrepresent Justyce as a “thug,” which angers SJ. Surprisingly, Jared wants to help correct the misguided impression of Justyce. Doc encourages Justyce to focus on the kind of man he wants to be, and SJ apologizes to Justyce for avoiding him.
Manny’s father is forced to step down from his corporate VP role because of his efforts to get justice for Manny and Justyce, and Manny’s parents decide to move. Feeling alone, Justyce visits the leader of the Black Jihad but decides not to join the gang. Instead, he goes to see SJ, and the two confess their feelings for each other. The news reports arson at Officer Tison’s home. After his graduation, the police question Justyce in connection with the fire because some Black Jihad have named Justyce as an accomplice. But Justyce has an alibi: He was with SJ’s family the night of the fire.
When Justyce’s mother learns he’s dating a white girl, she becomes upset. At the trial for Manny’s murder, the defense attorney cross-examines Justyce, trying to paint Justyce and Manny as volatile and violent. The jury doesn’t reach a conclusion about the murder charges against Officer Tison. Before there can be a retrial, Tison is murdered in prison. Several weeks later, Justyce and SJ head to college. In a final Dear Martin letter, Justyce talks about being negatively judged by his college roommate. He also reflects on why his be-like-Martin experiment didn’t work. Justyce realizes he needs to figure out who he is and what he believes. Four months later, Justyce reconnects with Jared at Manny’s grave. The two talk about missing Manny, life at Yale, and what they plan to study. It’s clear Jared has changed and that a genuine friendship has begun between the two.