An unnamed Stranger arrives in the small border town of San Miguel, where he encounters Silvanito, the local innkeeper. Through their conversation, the Stranger learns about a violent feud between two smuggler families striving for dominance in the town: the Rojo brothers—Don Miguel, Esteban, and Ramón—and the Baxter family, which includes the town sheriff John Baxter, his matriarchal wife Consuelo, and their son Antonio. Seizing the opportunity for profit, the Stranger devises a plan to manipulate both factions against one another. He establishes his lethal prowess by effortlessly gunning down four men upon entering the town, thus earning the attention of both families.
Witnessing the brutal slaughter of a group of Mexican soldiers transporting gold meant for rifles, the Stranger hatches a cunning scheme. He bodies the two fallen soldiers at a nearby cemetery, making it seem as though they might still be alive. He then sells this fabricated information to each faction, convincing them that two soldiers survived the ambush. This incites a race to the cemetery: the Baxters aim to extract testimony from the supposed survivors against the Rojos, while the Rojos seek to eliminate any threats to their reign. The ensuing chaos concludes with Ramón "killing" the supposed survivors, and Esteban capturing Antonio Baxter.
While the two families engage in their lethal duel, the Stranger utilizes the distraction to infiltrate the Rojo hacienda in search of gold—only to accidentally knock out a woman named Marisol. The Stranger brings her to the Baxters, who agree to trade her back to the Rojos in exchange for Antonio. During this tense hostage exchange, Marisol's family approaches her, but Ramón orders his man Rubio to execute Marisol's husband, Julio. However, Silvanito and the Stranger intervene just in time. The Stranger instructs Marisol to return to Ramón and insists that her husband take their son home, learning later from Silvanito that Ramón had taken Marisol as collateral over a cheating accusation.
As the night unfolds, the Rojos celebrate, unaware of the Stranger's plans. He eliminates their guards, frees Marisol, and wreaks havoc in the house she was held captive to mislead the Rojos into thinking it was an onslaught by the Baxters. He provides Marisol with some money and advises her family to leave the dangerous town.
But soon after, the Rojos deduce that it was the Stranger who liberated Marisol and subsequently capture him. After enduring torture, the Stranger escapes, only to witness the Rojos viciously set fire to the Baxter home, indiscriminately killing its occupants—including women and children—who attempt to flee the flames. With the help of Piripero, the local coffin maker, the Stranger sneaks out of town by hiding in a coffin and recuperates in an abandoned mine.
When he learns from Piripero that Silvanito has been captured and tortured for information about him, the Stranger returns to confront the Rojos. Donning a steel chest plate concealed under his poncho, he dares Ramón to "aim for the heart." As Ramón’s bullets fail to penetrate, the Stranger calmly disarms him and takes out Don Miguel, Rubio, and the remaining Rojo henchmen. He then uses his final shot to free Silvanito from his hanging restraint.
In a classic showdown, the Stranger challenges Ramón to reload faster than he can fire his revolver, ultimately killing him. Just as Esteban Rojo aims for the Stranger’s back from a safe distance, he meets his demise at the hands of Silvanito. With the dust settling, the Stranger bids farewell to Silvanito and Piripero before riding away from a town steeped in bloodshed and chaos.
