The book tells us the story of Demetrio Macías, a peasant who, after having a misunderstanding with a local cacique (land owner), is hunted by national government soldiers (Federales) and decides to flee when they arrive at his home and kill his dog, prompting him to abandon his family and take revenge. He escapes to the mountains and forms a group of rebels who support the Mexican Revolution.
The whole novel has various reading levels and the character names represent forces or ideals beyond the characters themselves. Some of them are prototypes of the kind of people that were dragged into the revolution, like Demetrio, whose name is associated with the goddess of farming and agriculture Demeter; La Pintada (translated as War paint) a tough woman; and Camila, a teenager peasant who is dragged into the conflict by means of subterfuge to become Macías's lover. Others symbolize revolutionary hopes and conflicts, like Luis Cervantes, an educated man (whose name evokes Miguel de Cervantes) mistreated by the Federales and therefore turning on them, and Güero Margarito, a cruel man who finds justification for his deeds in the turbulence of the times. Macías's dog, killed at the beginning, is a symbol of peace, fittingly named Palomo (dove).
With a concise, unsympathetic tone, Azuela takes the reader along with this band of outcasts as they move along the hills of the country, seemingly struggling for a cause whose leader changes from day to night. The rebels, not very certain of what or whom they are fighting for, practice the abuse and injustice they used to suffer in the hands of the old leaders. So the Mexican people, as the title of the book hints, are always the "ones below", no matter who runs the country.
In the end, Macías has lost his cherished ones and most of his men, and reunites with his family with no real desire or hope for redemption or peace. He has forebodings of his destiny, and the last scene of the book leaves him firing his rifle with deathly accuracy, alone and extremely outnumbered by his enemies.
