Nightjohn by Gary Paulsen is set in the South before the Civil War. The story is narrated by Sarny, a slave on the Waller plantation. One day while Sarny is outside the big house, she overhears Waller’s wife complaining that her husband has spent $1,000 on a new slave. Sarny is intrigued but knows better than to ask any questions. The next day, she sees this new slave named John attached to Waller’s horse cart pulling his new master back home. Waller is a cruel master who regularly beats his slaves. Waller has stripped John naked and forced him to run through the dirt, pulling the cart by his neck. Immediately, Sarny sees the scars that criss-cross new slave's back. She wonders why Waller would buy a slave that is obviously difficult to train.

That night, in the sleeping barracks, John calls out and asks if anyone has any tobacco to trade. Knowing that John came it naked, Sarny knows that he obviously has nothing to trade; but, at the same time, she is intrigued by his question. She remembers the tobacco she still has stored in her pocket. She asks John what he could possibly trade. He promises to trade her letters, the knowledge of reading and writing. Sarny knows nothing of letters or numbers, except that they are dangerous. Still, she takes John up on his offer. For the next few nights, Sarny and John meet in the middle of the night, when the rest of the slaves are asleep. John traces letters into the dirt teaching Sarny what they look and sound like. From these evening meetings, John earns the nickname “Nightjohn.”

One evening Sarny’s caretaker, an older woman called Mammy, overhears John’s reading lesson. Enraged, she beats John and demands to know why he’s putting Sarny is such danger. Slaves caught learning to read or write were beaten, tortured, or killed. John tells Mammy his story. After suffering years of torture and abuse, he ran from his previous owner and made it all the way North. There, he learned to read and write. Empowered, he traveled back to the South to teach other slaves, holding secret night classes at various plantations and escaping to safety before the sun rose. Eventually, he was caught again and sold to Waller. Despite the danger, John passionately seeks to educate the slaves so they can document their histories and create empowered futures. After hearing this, Mammy silently agrees to let the lessons continue.

At the same time, Waller continues beating, torturing, and inadvertently murdering his slaves, which adds to the tension around the plantation. One afternoon, he sees Sarny scratching a word into the dirt and furiously begins beating her. He demands to know who is teaching Sarny to read, but she refuses to tell about John. Enraged, Waller begins brutally whipping Mammy. To stop the unfair torture, John steps forward and admits to teaching Sarny. As punishment for his crime, Waller chops off two of John’s toes. John spends a few days healing in the barracks. Then, in the middle of the night, he runs back to safety up north. Thinking she will never see John again, Sarny is surprised when he returns for her one night a few months later. He takes her to a secret camp where he is teaching slaves to read. The story ends with the knowledge that Nightjohn has returned. He will bring hope to the slaves.