"Captains of the Sand" refers to the street boys of Salvador, minors whose unruly and marginalized lives are generally explained by family tragedies related to poverty. The group of boys known as the Capitães hides in an abandoned warehouse on one of the beaches of the Bahian capital.

The central characters in the narrative each possess unique traits: João Grande has brute strength, the professor is remembered for his artistic talent, Sem-Pernas embodies existential bitterness, Volta-Seca represents the oppression of the countryside, Gato reflects precocious sexuality, Boa-Vida is the streetwise hustler, and Pirulito exhibits a tendency towards religiosity. They are all led by Pedro Bala, the protagonist of the novel.

Orphaned at a young age, Bala learns about his father's past as a labor leader who was murdered during a strike. This information comes from João de Adão, an organizer of strikes who opens the doors of labor struggle for the boy. However, Bala prefers to continue orchestrating the robberies and thefts committed by the gang, participating in the most dangerous actions. One day, a girl named Dora joins the group; her parents had died from a malaria epidemic. Initially met with suspicion, Dora gradually integrates into the group, earning everyone's respect and Pedro Bala's love.

During a robbery, Bala and Dora are arrested. She is sent to an orphanage, while the boy endures violence from torturers attempting to extract the location of the Capitães' hideout. Bala suffers but reveals nothing. He escapes from the reform school and rescues Dora. However, she leaves the institution in poor health. On her last night alive, she asks her boyfriend to make love to her.

Dora's death coincides with a turning point into adulthood for the main members of the gang. João Grande becomes a sailor, Volta-Seca turns into a cangaceiro (a bandit of the Brazilian hinterlands), Pirulito joins a religious order, and Sem-Pernas commits suicide to avoid falling into the hands of the police. In the end, Pedro Bala leaves the group but not his role as a leader, now focused on labor life. In this way, he continues the unfinished work of his father.