The Bottom is a mostly black neighborhood in Ohio. A good white farmer promised freedom and a piece of Bottom land to his slave if he would perform some very difficult chores. When the slave completed the work, he asked the farmer to keep his end of the bargain. Freedom was easy, the farmer had no objection to that, but he didn't want to give up any land, so he told the slave that he was very sorry that he had to give him valley land. He had hoped to give him a piece of the bottom land. The slave blinked and said he thought valley land was bottom land. The master said, "Oh no! See those hills? That's bottom land; rich and fertile."
Shadrack, a resident of the Bottom, fought in World War I. He returns a shattered man, unable to accept the complexities of the world; he lives on the outskirts of town, attempting to create order in his life. One of his methods involves compartmentalizing his fear of death in a ritual he invents and names National Suicide Day. The town is at first wary of him and his ritual, then, over time, unthinkingly accepts him.
Meanwhile, the families of the children Nel and Sula are contrasted. Nel is the product of a family that believes deeply in social conventions; hers is a stable home, though some might characterize it as rigid. Nel is uncertain of the conventional life her mother Helene wants for her; these doubts are hammered home when she meets Rochelle, her grandmother and a former prostitute, who is the only unconventional woman in her family line. Sula's family is very different: she lives with her grandmother Eva and her mother Hannah both of whom are seen by the town as eccentric and loose. Their house also serves as a home for three informally adopted boys and a steady stream of boarders.
Despite their differences, Sula and Nel become fiercely attached to each other during adolescence. However, a traumatic accident changes everything. One day, Sula playfully swings a neighborhood boy, Chicken Little, around by his hands. When she loses her grip, the boy falls into a nearby river and drowns. They never tell anyone about the accident even though they did not intend to harm the boy. The two girls begin to grow apart. One day Sula's mother's dress catches fire and she dies of the burns. Eva, her mother, sees her from the window and jumps out into the garden.
After high school, Nel chooses to marry and settles into the conventional role of wife and mother. Sula follows a wildly divergent path and lives a life of fierce independence and total disregard for social conventions. Shortly after Nel's wedding, Sula leaves the Bottom for a period of 10 years. She has many affairs, some, it is rumored, with white men. However, she finds people following the same boring routines elsewhere, so she returns to the Bottom and to Nel.
Upon her return, the town regards Sula as the very personification of evil for her blatant disregard of social conventions. Their hatred in part rests upon Sula's interracial relationships, but is crystallized when Sula has an affair with Nel's husband, Jude, who subsequently abandons Nel. Ironically, the community's labeling of Sula as evil actually improves their own lives. Her presence in the community gives them the impetus to live harmoniously with one another. Nel breaks off her friendship with Sula. Just before Sula dies in 1940, they achieve a half-hearted reconciliation. With Sula's death, the harmony that had reigned in the town quickly dissolves.