Plot
During the Mexican Revolution, a Durango-bound government munitions train is forced to stop due to the presence of a crucified federal army officer on the tracks. El Chucho/Chuncho Muños, an arrogant gun runner and guerrilla figure who is loyal to the Zapatist revolutionary leader General Elías, leads his gang in an assault on the train. Lieutenant Alvaro Ferreira, who is commanding the rurales' escort of the train, attempts to save the officer, but after being fatally wounded by Chuncho he orders the train to run the captain and him over to escape the bandits. Bill Tate, a quiet and mysterious American passenger on the train, kills the engineer and stops the train again, allowing Chuncho and his gang to kill the remaining rurales and take their weapons. Posing as a former prisoner of the army, Tate joins the gang and is quickly befriended by Chuncho, who nicknames him "Niño" (which means "Kid" in Spanish).
After several heists, the gang travels to the town of San Miguel, where Chuncho meets with his old friend Raimundo to overthrow the weakhearted town boss, Don Felipe. Rosaria, Felipe's spirited wife, attempts to defend him; when Chuncho's men assault her, Tate angrily berates them for their behavior. Chuncho shoots Guapo, a gang member, for attempting to kill Tate during the discussion. Don Felipe is made to drive Chuncho and his gang back to San Miguel, and he is eventually executed.
Chuncho prepares to stay in San Miguel, drilling the villagers in the hopes of becoming a General himself; Tate convinces much of the gang to leave San Miguel so they can sell their weapons to Elías. Eventually missing his bandit lifestyle, Chuncho leaves San Miguel under the care of El Santo, his priestly half-brother, on the pretext of recovering a gold-plated Hotchkiss M1914 machine gun from his former gang. After killing one of them, Picaro, Chuncho resumes leadership of the others, hoping to sell the weapons to Elías before returning to San Miguel.
Elías' emissary arrives but is pursued by the Mexican army troops. Tate and Chuncho use the machine gun to decimate the troops, but nearly all of Chuncho's remaining gang is killed in the firefight. Unseen by the others, Tate also kills the emissary. Adelita, Chuncho's last surviving loyal gang member, abandons the pair after her lover, Pepito, is killed in the battle. During the ride to Elías' camp, Tate falls victim to a malaria attack. While getting quinine pills for Tate, Chuncho finds a golden bullet among his possessions; Tate later claims that the bullet is a good luck charm. Soon after, Chuncho decides to leave San Miguel with "El Niño" so they can sell their new guns and a cannon to General Elías. Chuncho's adopted brother, the hunchbacked former priest and guerrilla fighter known as El Santo, admonishes Chuncho for his overt greediness and insists to his brother that he must return quickly before the Federales/Mexican army attacks the unprotected town.
Chuncho and Tate arrive at Elías' camp after two days, where they encounter several starving revolutionaries. Chuncho sells the guns and is paid five thousand pesos before learning from Elías that the people of San Miguel were massacred by the army while he was away. Realizing his irresponsibility, Chuncho allows himself to be taken away to be executed by Santo, the sole survivor of the attack. Meanwhile, Tate, from a high vantage point, shoots Elías first and then quickly kills El Santo before Chuncho's sentence can be carried out. Tate escapes as Elías' doctors pronounce his death: shot in the head with a golden bullet.
Weeks later, Chuncho, now an impoverished beggar, tracks Tate to a hotel in Ciudad Juarez and tries to shoot him. Tate, insisting that he has been waiting for him, gives him a half-share of the reward he received from the Mexican Government for assassinating Elías: 100,000 pesos in gold. Chuncho, astonished by Tate's apparent loyalty and friendship, visits a barber, a tailor and a brothel.
The next morning the pair prepare to leave for a new life in the United States. However, when Chuncho watches as Tate cuts through a line to buy their train tickets, he begins to reconsider their relationship and his responsibilities. Learning that he had been further manipulated by Tate through his pretending to be an army prisoner, Chuncho suddenly declares that, although they are friends, he must kill him. Tate asks why, to which Chuncho replies "¿Quién sabe?", [Note 1] before shooting Tate dead while he is boarding the slowly moving train. The police arrive at the station and Tate's body begins its return to the United States while Chuncho, laughing maniacally, tosses his bag of money to a group of peasants near him and flees from the authorities down an external corridor of carriages, happily shouting and exhorting the poor to buy dynamite instead of bread.
