The Prologue describes the changes taking place in the once all- Black neighborhood known as the Bottom in the hills above the once all-white town of Medallion, Ohio. The old buildings that once functioned as the site of a vibrant African-American community are leveled to make way for a golf course as rich white people begin to encroach on the Bottom.
Local folklore has it that the Bottom received its name from a slave owner's greedy deception of a slave. The slave owner promised the slave that he would free him if he completed some difficult tasks. In addition, he promised the slave a plot of good "bottom land" in the valley. When the time came, the slave owner didn't want to part with any of his good land. He gave the slave a plot in the hills, stating that it was the "bottom of heaven" because it was closer to God. The slave was delighted to accept the "gift." Only later did he realize that hilly land was extremely difficult to farm.
In 1917, 20-year-old Shadrack suffers a traumatic experience in World War I. Afterward, he awakes in a veteran's hospital to find a tray of food. He is comforted to see that food items are neatly contained in separate compartments. When he tries to eat, he is horrified to see his hands growing rapidly. When a male nurse tries to force him to eat, Shadrack fights back in hysteria. After he is placed in a straitjacket, he is "relieved and grateful" because he doesn't have to look at his hands. He longs to see his face, but, confined as he is, it isn't possible.
Shadrack is released from the hospital a year later because his ward is short on space. He is later picked up by the police as he sits on the roadside crying. In his jail cell, he looks at his reflection in the toilet bowl. He is relieved to find that he does indeed exist. The sheriff sends Shadrack to his home town, the Bottom, with a farmer.
Shadrack is terrified that he might die unexpectedly. He institutes a self-proclaimed National Suicide Day as a means of coping with his fears. Every January 3rd, Shadrack marches through town ringing a cowbell and carrying a hangman's rope. He shouts that people should kill themselves or each other if they want to. The residents are disturbed at first, but eventually National Suicide Day infiltrates the consciousness of the community, becoming a part of the routine of their lives.
Helene Wright, the daughter of Rochelle, a Creole prostitute, from New Orleans, was raised by her strict, religious grandmother, Cecile. Helene was safely married off at 16 to Cecile's great nephew, Wiley Wright. They built a respectable life in the Bottom where Helene becomes a member of the most conservative church. After nine years of marriage, Helene gives birth to her only child, Nel. She raises Nel under the same strict rules that governed her own childhood.
When Cecile falls ill, Helene sews herself a magnificent dress in preparation for the journey she will have to make to New Orleans in the Deep South for the funeral. Despite the splendor of her clothes, she is insulted and humiliated by the white conductor on the train. She gives the conductor a dazzling smile, inciting the silent animosity of the Black passengers. When she and Nel arrive in New Orleans, they discover that Cecile has already died. To Helene's discomfort, she finds Rochelle at Cecile's house. Nel is profoundly affected by her brief encounter with Rochelle.
Helene is displeased when Nel befriends Sula, a girl with a birthmark over one of her eyes, because Hannah, Sula's mother, has a loose reputation. However, Helene comes to accept the relationship because Sula seems well behaved when she visits Helene's immaculate home.
Throughout Sula, things are not quite what they appear to be. The town of Medallion, with its rich, fertile fields, appears to be a more desirable place to live than the Bottom. The demolition of Bottom's old shacks to make room for a pristine golf course seems like an improvement. However, Morrison states the Bottom was once a vibrant community filled with laughing voices and a parade of unique, interesting people. The building of the golf course is in fact the displacement of a vibrant community; it is an example of homogeneity encroaching upon what was once unique.
Shadrack is suffering from severe shell shock. The horrors of the war annihilated the boundaries that once circumscribed his perception of reality, as can be seen in his weird sense that his hands are growing out of control. The world now seems to him a thing of chaos, and he is unable to deal with the excess of choices and paths it leaves open to him. In response to his fears, Shadrack develops an intense need to order his own existence. Suicide Day is an aspect of this effort: it is Shadrack's attempt to compartmentalize his fear of death into a single day. The need to "order and focus experience" is an important theme in Sula. Many of the major characters struggle to extract an ordered meaning from the events in their lives.
While Shadrack illustrates the terror of chaos, Helene illustrates the problems inherent in excessive order. Morrison suggests that much order breeds repression because it stifles an individual's personality. Celine raised Helene under the strict conventions of religion. She wanted to crush any spark of the wildness and independence that characterized Rochelle. Helene obeyed this imperative to conform by settling into an unremarkable middle class life. She later tries to force that same repressive order onto her daughter, Nel. In a sense, the pressure of dullness and sameness that Helene imposes on her daughter echoes the dullness and sameness that overtakes the Bottom decades later when rich whites move into the area and build their pristine golf course.
Though Helene's conventionality is implicitly linked to the rich whites of Medallion, Helene still suffers from racism, as can be seen by her experience on the train. The order and boundaries of her conservative, religious, middle class respectability do not protect her from racism. Helene tries desperately to maintain composure, but her dazzling smile has a hollow, disturbing implication. She inadvertently gives her approval to a biased, racist authority, inciting the anger and hatred of the other passengers. Her effort to placate and please the rude conductor only makes his sense of superiority more secure.
Nel realizes that her mother is not indomitable when she senses Helene's struggle to maintain her composure. She likens her mother's insides to custard, a weak, runny food. After meeting Rochelle, Nel realizes that there are women who defy the conventional boundaries, whether of religion, femininity, or race. Struck by the realization that convention does not necessarily equate to strength, Nel resolves to build herself according to her own rules, to find strength within herself.