A stranger arrives at the little Mexican border town of San Miguel. Silvanito, the town’s innkeeper, tells the Stranger about a feud between two families vying to gain control of the town: on the one side, the Rojo brothers: Don Miguel, Esteban and Ramón; on the other, the family of the town sheriff, John Baxter. The Stranger decides to play each family against the other in order to make money, and proves his speed and accuracy with his gun to both sides by shooting the four men with ease who teased him as he entered town.
The Stranger seizes his opportunity when he sees the Rojos massacre a detachment of Mexican soldiers who were escorting a shipment of gold. The Stranger takes two of the dead bodies to a nearby cemetery and sells information to both sides, saying that two Mexican soldiers survived the attack. Both sides race to the cemetery, the Baxters to get the “survivors” to testify against the Rojos, the Rojos to silence them. The factions engage in a gunfight, with Ramón managing to “kill” the “survivors” and Esteban capturing John Baxter’s son, Antonio.
While the Rojos and the Baxters are fighting, the Stranger searches the Rojo hacienda for the gold. While he is searching he accidentally knocks out a woman, Marisol. He takes her to the Baxters, who, in turn, arrange to return her to the Rojos in exchange for Antonio. During the exchange, Marisol’s son runs to her, with her husband following. While the family embraces, Ramón orders one of his men, Rubio, to kill her husband as he has already told him to leave town. Silvanito attempts to protect the family with a shotgun, but is about to be killed himself when the Stranger backs him up, staring down Rubio. Neither Ramón nor any of his men attempt to challenge the Stranger, knowing that he is too fast on the draw.
The Stranger then tells Marisol to go to Ramón and for her husband (Julián/Julio) to take their son (Jesús) home. Afterwards, the Stranger learns from Silvanito that Ramón had taken Marisol from her husband and forced her to live with him as his prisoner. That night, while the Rojos are celebrating, the Stranger rides out and frees Marisol, shooting the guards and wrecking the house in which she is being held in order to make it appear as though it were attacked by the Baxters. The Stranger gives Marisol, her husband, and their son some money and tells them to leave the town. When the Rojos discover that he freed Marisol, they capture the Stranger and torture him, but he escapes. Believing the Stranger to be protected by the Baxters, the Rojos set fire to the Baxter home and massacre the entire family as they run out of the burning building. Ramon kills John Baxter and Antonio after pretending to spare them. Consuelo, John Baxter’s wife, appears and curses the Rojos for killing her husband and son, as they were unarmed. She is then shot and killed by Esteban.
With help from Piripero, the local coffin-builder, the Stranger escapes town by hiding in a casket. The Stranger hides and convalesces in a nearby mine. When Piripero tells him Silvanito has been captured, the Stranger returns to town and faces the Rojos. With a steel chest-plate hidden beneath his poncho, he taunts Ramón to “aim for the heart” as Ramón’s rifle shots bounce off. Ramón uses up all of his bullets this way. The Stranger shoots the rifle from Ramón’s hand and kills the other Rojos standing nearby, including Don Miguel and Rubio. He then uses the last bullet in his gun to free Silvanito, who had been tied hanging from a post. The Stranger challenges Ramón to reload his rifle faster than he, the Stranger, can reload his pistol. The Stranger shoots and kills Ramón. Esteban Rojo aims at the Stranger from a nearby building, but is shot dead by Silvanito. The Stranger bids farewell and rides away from the town.