In the late 1930s, amidst the Depression, the Thomas family resides in a single room tenement apartment in the South Side ghetto of Chicago during winter. One morning, a large rat is spotted by Bigger Thomas' mother and sister, causing them to become fearful. Bigger attempts to kill the rat multiple times using an iron skillet and finally manages to succeed on the third attempt.

Bigger taunts his sister Vera with the bloody carcass, which leads her to faint, and his mother reprimands him for being cruel and insensitive. The family is on welfare, and the relief agency has given Bigger a job offer, warning that they will stop providing food assistance to the family if he refuses to take the job. Despite his reluctance, Bigger agrees to meet with Mr. Dalton, who could potentially become his employer.

Bigger heads to a nearby poolroom where he's scheduled to meet his buddies Gus, G.H., and Jack. The group has been discussing a plan to rob a local deli called Blum's for months, but they're all too frightened to follow through with it, mainly because the owner is white. Bigger, who is also scared but doesn't want to admit it, teases Gus about his cowardice, hoping that he will be deterred and cancel the plan. Nevertheless, Gus agrees to proceed with the robbery, and they all agree to meet up at the poolroom at 3 p.m.

Bigger and Jack depart from the poolroom and head to a cinema, where they engage in masturbation in the dimly lit surroundings prior to the start of the film. The initial segment of the movie is a newsreel depicting affluent, single, young women of high society known as "debutantes" vacationing in Florida. Mary Dalton, the daughter of Mr. Dalton, appears in the newsreel, and as Bigger and Jack stare at her while she frolics on the beach in a swimsuit, they discover that she has recently caused a scandal with her parents by dating a communist.

After watching the sensational movie Trader Horn, Bigger and Jack leave to get their guns for the planned robbery. Later, they both meet G.H. at the poolroom where Gus arrives last. Bigger immediately attacks Gus with a knife, projecting his own fears of robbing a white man onto him. Gus manages to escape and the robbery plan falls apart. G.H. comments that this is likely what Bigger wanted. The poolroom owner, Doc, then ejects Bigger from the establishment.

Afterward, Bigger heads to his job interview via streetcar, which takes him to the affluent, predominantly white neighborhood where the Daltons reside. In an effort to feel more secure, he brings along his gun. Upon arrival, he is greeted by Peggy O'Flagherty, the Daltons' cook and housekeeper, and subsequently meets Mr. Dalton and his wife, who is frail and visually impaired. Bigger is anxious and restless as Mr. Dalton inquires about his background. It is disclosed that Bigger had previously been sent to a reformatory for stealing tires. Nevertheless, Mr. Dalton offers him the position of the family's chauffeur, with a generous salary of $25 per week, plus lodging and meals.

Bigger agrees to take the job, but at that moment, Mary Dalton shows up and begins discussing the benefits of joining a union, which causes Bigger to worry that he may be fired. Mary's politically provocative comments make Bigger feel uneasy. Shortly after Mary departs, Mr. Dalton reveals to Bigger that he supports the NAACP, a moderate group committed to enhancing the social and economic standing of African Americans. Bigger has never heard of the organization.

Peggy O'Flagherty informs Bigger at a later time that Mr. Dalton has made a donation of five million dollars to support education for African Americans, which conflicts with Bigger's belief that Mr. Dalton is the primary owner of Chicago's poorest neighborhoods. Peggy says that as an Irish person, she understands how Blacks are treated in America. Peggy treats Bigger to a scrumptious meal and instructs him on how to maintain the mansion's sizable basement furnace, which will be one of his responsibilities. Bigger then proceeds to his cozy new room and unwinds, feeling satisfied prior to starting his initial task.

Bigger is tasked with chauffeuring Mary Dalton to a lecture at the University that evening. However, on his way to the garage, he runs into Mrs. Dalton who expresses her desire for Bigger to return to school someday. Bigger is acutely aware of himself and feels uneasy in the presence of white people, particularly Mary Dalton who he finds to be erratic and disconcerting. After getting into the car, Mary informs Bigger that they will not be going to the University as planned. Instead, she asks him to drive her to meet her Communist boyfriend, Jan Erlone.

Jan is more determined than Mary to treat Bigger as an equal and disregards many racist taboos by shaking Bigger's hand, requesting to be called by his first name, and insisting on driving to their next location while sitting next to Bigger with Mary.

Jan and Mary express their desire to eat in the ghetto, and Bigger guides them to a restaurant called Ernie's Kitchen Shack located on the South Side. Upon reaching the restaurant, Jan and Mary insistently request Bigger to join them for the meal, but Bigger agrees with great reluctance. Upon entering the restaurant, Bigger's girlfriend, Bessie Mears, greets him, but he feels uneasy and pays little attention to her.

Jan asks Bigger about his upbringing, and Bigger discloses that he grew up in the Southern United States and implies that his father was killed by a group of white people. Jan and Bigger then talk about communism, and Jan brings up the Scottsboro case. They drink beer and later switch to rum while eating. Mary informs Bigger that she will be leaving for Detroit the following day, and requests that he take her trunk and drive her to the train station in the morning.

After leaving the restaurant, everyone keeps drinking from the rum bottle while Bigger drives and Jan and Mary have a political conversation in the back seat. Mary enthusiastically offers to provide bail money for some Communists who got arrested, and then confides in Jan that she plans to join the Communist Party soon. She explains that she wants to focus on working with Black people because they are the most marginalized group in society.

At this moment, Bigger is experiencing a warm sensation due to the rum, while Jan and Mary are both heavily under the influence of alcohol. The pair engages in kissing and touching in the back seat, and Bigger tries to resist becoming sexually aroused. After a while, Jan checks the time and realizes it's already 1 a.m., so he decides to leave. Bigger drives Jan close to his home, and before parting ways, they all take one final sip from the rum bottle. Jan provides Bigger with some communist reading material and bids him farewell.

Mary, who was very drunk, sprawls across the front seat and rests her head on Bigger's shoulder. Upon reaching the Dalton house, Mary is unconscious, and Bigger must awaken her and assist her to her bedroom. He picks her up and carries her towards the house, feeling a sense of terror at the thought of being seen touching a white woman, but this fear is somewhat lessened by the alcohol. His emotions fluctuate between fear and sexual excitement. Once they reach Mary's darkened bedroom, Mary and Bigger kiss. Mary responds by rubbing against him. Bigger fondles her breasts, but their intimate moment is interrupted by the sudden appearance of blind Mrs. Dalton at the door.

When Mary starts to mumble semi-consciously, Bigger becomes overwhelmed with fear and tries to prevent Mrs. Dalton from discovering him by covering Mary's head with a pillow to silence her. As Mary struggles, Bigger presses the pillow down harder. However, when Mrs. Dalton approaches, she smells the scent of alcohol in the air and recoils, accusing Mary of being drunk. Bigger is initially relieved when Mrs. Dalton leaves, but he later realizes that Mary has died from suffocation.

Despite feeling extremely afraid, he relies on his strong survival instincts to devise a strategy to evade getting caught. He is aware that killing a white girl, regardless of the situation, would lead to his inevitable demise. Therefore, he starts contemplating a plan to frame Jan and the Communists for the crime. In addition, he takes the half-packed luggage, which Mary intended to take on her journey to Detroit, puts the dead body inside the trunk, and transports it downstairs to the basement.

Upon arriving at the location, he makes the decision to incinerate the corpse using the furnace. He proceeds to insert Mary's body, but her head proves to be too large. To resolve this issue, he employs a knife and hatchet to detach her head, which he then throws into the fire. His intention is to fabricate a story in which he claims that he and Jan escorted Mary back to her residence, and that he last saw them kissing in the vehicle, which remains parked in the driveway. During his inspection of the car, he discovers Mary's handbag, which contains a significant amount of cash. He decides to retain possession of the purse before returning to his mother's apartment, where he plans to transport the trunk to the train station the following day.

Bigger gets into his bed, and thinks, “They can’t say I did it. If they do, they can’t prove it”.