The novel is framed as the reminiscence of a female character (identified as Harriet Winslow through its course) "now she sits alone and remembers".
An embittered American writer and former journalist, not named until the final chapter as Ambrose Bierce, decides to leave his old life behind and seek death in the midst of the Mexican Revolution. A widower whose two sons are dead and whose daughter refuses to speak to him, he seeks out part of the Army of the North under Pancho Villa. The particular group he encounters in Chihuahua, led by 'General' Tomás Arroyo, has just liberated the massive hacienda of the Miranda family. Arroyo is mestizo, the product of the rape of his mother by his Miranda father, and is persuaded by the old gringo to let him join the revolutionary force.
At that same hacienda, the old man meets Harriet Winslow, a 31-year-old woman from Washington D.C., hired as a blind to tutor the Miranda children, while the family has fled the country. Harriet, however, refuses to leave the hacienda, insisting that she has been paid and will wait for the family's return. At first, she will not call Arroyo "General" (insisting that he has merely given himself the title), and has a patronizing view of the revolutionary army and the Mexican people. Her own father had disappeared during the earlier American invasion of Cuba and the Winslow family has been living off his army pension. Only Harriet knew that he had really stayed behind to live with a mulatto woman.
Harriet is committed into the care of the old gringo, who subsequently falls in love with her. The gringo displays considerable courage under fire, risking what seems like obvious death, and gains a reputation for valor. However, his refusal to obey Arroyo's order to shoot a captured Federal officer means that the 'General' could have him executed. Instead Arroyo shoots the officer himself, then parlays Harriet into a sexual relationship in return for sparing the gringo. Although Harriet appreciates their encounter, she cannot forgive his sexual arrogance. Arroyo's partner, a woman referred to as "La Luna", whom the Revolution has liberated from an abusive landowning husband, accepts his infidelity as necessary. But the gringo finds Harriet's sacrifice ironic, forcing him to reveal to her his real purpose in coming to Mexico. Instead, he now treats Harriet as a daughter in place of his estranged child, while she takes the old gringo in place of the father who has abandoned his family.
While Arroyo was away fighting in the mountains, Harriet had been attempting to rebuild and restore the hacienda and teach the women and children there. He, however, wishes to destroy his place of birth, remembering his humiliation there as the unrecognized son of the owner, and wins over the local peasants by posing as a true son of the people and using the name of his mother (Arroyo) rather than Miranda, to which he has a right. That right he believes contained in a document which he keeps close to him (though he cannot read it), until the gringo sets it on fire in revenge for his treatment of Harriet. Arroyo then responds by fatally shooting him in the back.
Later, Harriet presses for the return of the gringo's body, claiming him as her father, so that he may be buried in the grave reserved for the vanished Winslow at Arlington National Cemetery. Pancho Villa now faces criticism for an alleged cold-blooded murder of an American by troops under his overall command. Villa has the American's body exhumed and 'executed' by firing squad (passing it off as the work of the Federales). When Arroyo approaches to give the dead body the coup de grâce, Villa orders the firing squad to shoot Arroyo as a means of preventing any further American response.
After Harriet crosses the border back to the US, she refuses to testify in front of Congress as part of a journalistic campaign to encourage the U.S. to 'civilize' Mexico, and decides that instead of attempting to change Mexico, as she had wanted to earlier, the better approach, as she now tells the waiting journalists, is "to learn to live with Mexico".
