The Holbrooks, a poor working family, live in a mining town. Jim works in the mine. Every morning, his six-year-old daughter Mazie (along with the rest of the town) wakes up to the sound of the mine whistle. During the morning this is a call for all the miners to get up and go to work. If it rings during the day, it means that one of the workers has been killed.
One morning, Anna Holbrook, Mazie's mother, worries about the new fire boss, whose carelessness may create a massive explosion and kill many of the miners. Mazie, outside, talks to herself how the mine is the "bowels of the earth" and the coal makes people black inside.
The narrative is interrupted by the story of Andy Kvaternick, a young mine worker, new on the job. The narrator tells how Andy's life will be one of frustration, deprivation, and danger. When the narration returns to the Holbrooks, we learn how their family life is in trouble. Jim, who drinks heavily, beats Anna and the children. Anna also beats the children, and the entire household exists in a state of tension. One night Mazie follows her father into town at night; the trip almost ends in disaster when a ruined miner, Sheen McEvoy, tries to throw Mazie down the mine shaft. He is stopped by a night watchman and Mazie lies in a fever for days afterwards.
Jim decides to move the whole family east in the spring, in order to do farm work. They scrimp and save for months. Meanwhile the town continues to fear that the new fire boss' carelessness will cost them their lives in the mines. The feared explosion happens one day in November. Jim is missing, but he returns, in a state of serious agitation, after five days.
The family finally leaves in April, after many delays and hardships. They have a pleasant journey across Wyoming and Nebraska. In the Dakotas, a serious storm cripples their wagon, and they are immobile for two days. When they find the farm they will be working on, they are overwhelmed by its beauty and serenity.
At first, farm life is a great improvement over the mine. Although their neighbor, Benson, warns them about the insecurity of tenant farming, they have food on the table and the children are growing healthy with the fresh air. Mazie and Will go to school for the first time. Mazie meets Old Man Caldwell, an educated man who gave up his fortune to live a simple life working with the earth. He takes Mazie under his wing and tells her about the stars and the universe. He also explains politics and economics to Anna. When he is lying on his deathbed, he tries to impart some of his wisdom on Mazie. Failing that, he gives her some of his books. That effort also fails when Jim sells the books in town.
Farm life sours as Jim learns the harsh realities of tenant economics. After spending a year working hard, he still owes the farm owner. The winter descends on a tense Holbrook house. The situation is made worse by the freezing weather; the entire family must spend the day huddling around the kitchen stove. Anna, pregnant again, lives as if in a stupor: she does not do the housework or care for the children.
The household erupts over an incident involving the death of several newborn chicks. Jim and Anna hurl insults at each other; Jim leaves the house and does not return for ten days.
Early in March, Anna goes into labor. Mazie, nauseous, stays with her mother until Jim returns with the midwife. Then she flees into the manger and stays there, vomiting, until her father carries her back in. The child, Bess, is fine, and Anna is fine as well. After Bess is born, the family packs up and moves on again.
They set up their household in an urban slum near a slaughterhouse. The stench of the slaughterhouse pervades their home, the children's playing grounds, and every aspect of their lives. Mazie and Will return to school, but the new school is demoralizing and they are given a cold welcome. Unable to get on at the slaughterhouse, Jim finds a job with a sewer company. The work is difficult and the contractor is impossible. One of Jim's fellow workers, Tracy, quits. Another narrative passage told from a different perspective interrupts the main story to relate Tracy's tragic fate.
Meanwhile, the Holbrook family suffers from increasing deprivation and mental anguish. Ben is sick from the smell of the slum; Will is defiant, and Mazie wanders around in a daze, believing she is still on the farm. Anna feels paralyzed and is unable to meet her family's needs. The streets are violent and the children are terrified by the strange characters they meet and the hostility they encounter.
One night, Jim comes home drunk. He rapes Anna, who then suffers a miscarriage. For days she lies unmoving in bed, while the rest of the family struggles to care for the house, the baby, and themselves without her. When she wakes up and begins to move around, she compulsively cleans the house and is obsessed with germs and disease affecting the children. One of her neighbors comes to help her, but Anna is overwhelmed by everything: the poverty, the deprivation, the wild children, and the weight of not being able to secure a better place for them.
Anna recovers slowly and takes in laundry jobs to help make ends meet, despite Jim's disapproval. During rent week, she takes the children on a walk in search of dandelions - she will cook them so the family can have something green. But the lots in their neighborhood are full of unhealthy weeds, so they wander further and further into a middle-class neighborhood. Despite Mazie's concern - "Ma, we're going the wrong way," - Anna is in a dreamy mood and delights the children with games. They stumble on a lot overgrown with dandelions and fill three bags full. Anna begins to sing, and even Mazie is comforted - until a change in the wind brings the smell of the packinghouse their way. Then Anna snaps out of her dreamy mood and gathers the children up to go home again.
In July, Jim gets a new job at the slaughterhouse. This means a pay increase--to celebrate, he buys fireworks for the Fourth. Only Mazie, left out of the celebration because of her gender, sulks.
Things seem better at first. The children run wild, forgoing Anna's suggestion of the library. The children scavenge in the dump and steal from the ice truck. Mazie's new friend, an older girl named Ginella, introduces her to romances and exotic stories. Then a heat wave hits the slum. Conditions at the packinghouse are brutal; in the homes they are not much better. The children are ill and Mazie has nightmares.
On the worst day of the heat, Jim goes to work in the slaughterhouse, casings section. The workers are not allowed to slack off the work at all because of the heat. Many of them faint and slip; one worker has a heart attack. The company takes him away, docks his pay, and charges him for the company ambulance.
Although Anna needs her to help can peaches and apples, Mazie runs off to play in the morning. She meets up with other girls; they are snubbed by both Ginella and Will. Erina, a crippled, epileptic girl, appears and frightens the girls. She tells them about God and how the little children are meant to suffer. All the other girls run away and Mazie is left alone with Erina, until the twisted little girl finally leaves. Mazie feels ill from the encounter and goes to pick on her younger brothers.
As people all over the neighborhood suffer, Anna works alone and the children sleep. When Jim comes home, he goes straight for the water bucket and douses himself over and over without speaking to anyone; then falls asleep.
As night falls, Anna sings to Ben. The baby, Bess grabs ahold of a fruit-jar lid and begins slamming it down, over and over again. The family laughs, and then marvels when Will runs in the house with a homemade radio. They listen to the sounds for the first time. A dust storm rises outside. Anna, predicting an end to the heat wave, goes outside to wake Jim. At first he is too dazed to move, but then she insists that he come back in the house.