After his friend gets killed in World War II, Matthew Stratton, a young, white civics teacher, takes a substitute position at an all-Black school in New York City, determined to make a difference in his students' lives. In the first few days, Matthew gets acquainted with the school's administration and his students. Mr. Johnson, who's in charge of discipline, tells him that it will be tough, but Matthew tries to make the most of it. He tries to treat his students with respect and not over-enforce the rules, but he can tell that they don't quite trust him. He senses that they are all afraid of something, but he can't tell what. He takes special interest in a student named Johnny Boston, who he thinks will need a little extra help. After teaching for a few months, Matthew begins to see how the school operates, and he doesn't like it. The rowdy kids are the least of his concern. All of his fellow teachers, including his predecessor, had given up trying to teach the students anything. The school's principal embellishes his reports to the school board in order to get a bigger salary, though he doesn't care about the school at all. Mr. Johnson enlists the help of Mallory, a police officer, to intimidate and even beat the students into submission. One day, Mallory interrupts Matthew's class for an inspection, searching them for contraband. After seeing his students' reaction to this, Matthew feels like he needs to do something. He notices that Johnny Boston seems particularly alone after he was called out by Mallory. Matthew tries to speak up to the administration, but they ignore him. Matthew pays attention to his students and how they interact with each other outside of class. He learns that there are gangs within the school that make people pay for protection. One gang, the Hurricanes, is trying to recruit Johnny. Rahjah, a member of the Hurricanes, is particularly insistent. After Johnny refuses him, Rahjah tricks Johnny into going to an illicit craps game in the school's basement, saying that Johnny's younger brother is there and that Mallory is going to break it up. Johnny goes down but doesn't find his brother. When Mallory arrives, Johnny is the only student he catches. Johnny is out of class for a week after being beaten by Mallory and Mr. Johnson. Again Matthew complains to the principal, but to no avail. The next time Mallory comes into Matthew's classroom for an inspection, Matthew stands up to him and sends him away. He can tell that this act surprised the students, and he hopes that he's beginning to win their trust. Meanwhile, he learns that Johnny has joined the Hurricanes. One evening, Rahjah convinces Johnny to rob a store with him so that he can get a new suit. Johnny agrees, but only if they take a gun for protection. Johnny has Rahjah act as lookout while he breaks the storefront's glass with the butt of the pistol, but the police discover them anyway. Rahjah is able to slip away, but Johnny gets chased by the police onto the roof of a building. In the darkness he sneaks onto a fire escape, but he can tell the police are nearby. One tells him that he has been surrounded. Johnny recognizes the voice: it is Mallory. Filled with rage, Johnny shoots Mallory, but the knockback from the gun knocks him off the fire escape, and they both die. When Matthew hears the news, he is disheartened that he was never able to get through to Johnny. He considers heading back to his old teaching position at an easier school, but as he crosses the bridge back into the city, he realizes that he can never go back.