On the eve of her thirteenth birthday, Esperanza harvests grapes with Papa on the family's ranch in Aguascalientes. Papa is murdered by bandits that night. Her world ends before it has fully begun.

After Papa's murder, Tío Luis proposes marriage to Mama, offering to let her stay on the land. When she refuses, the uncles burn the main house. Mama, Esperanza, Hortensia, Alfonso, and Miguel flee by night toward a train that will take them to California.

On the train north, Esperanza discovers the hidden freight car compartment and the reality of migrant travel. She encounters poverty at close range for the first time — the smells, the crowding, the children with dusty feet. She meets Carmen and her family.

The group arrives in California and reaches the labor camp in the San Joaquin Valley. Esperanza is shocked by the conditions — dirt floors, shared outhouses, a company store that keeps workers indebted. She meets Marta, a labor organizer who challenges her.

Esperanza begins working in the camp, sweeping and watching the Montes twins while other women work in the fields. She struggles to learn basic domestic tasks — sweeping wrong, nearly dropping a baby. Her incompetence humiliates her.

Mama falls seriously ill with Valley Fever, a lung disease from the dust. She is hospitalized and cannot work. Esperanza must take over the full financial burden of the household. She also faces the threat of a labor strike that could get them all deported.

Esperanza harvests potatoes in the fields alongside adult workers. Isabel hopes to be Queen of the May at school — but is denied the honor because she is Mexican. Esperanza sends money to Mexico to bring Abuelita north. She crochets the zigzag blanket and thinks of valleys and mountains.

The final movement of the novel: the seasons turn again to grapes. Abuelita finally arrives. Mama recovers. Miguel, who left without explanation, returns — having spent Esperanza's savings to bring Abuelita north. Esperanza reaches into the earth and hears its heartbeat again. She rises.