In the turbulent landscape of 1913 Mexico, where revolution hangs in the air, outlaw Juan Miranda heads a gang of bandits. The story begins when he and his crew rob a coach filled with wealthy travelers, leading to a violent encounter that sees him assault a female passenger who dares to insult him. Amid this chaos, an Irish Republican explosives expert, John H. Mallory, passes by on his motorcycle. Juan, eager for wealth and power, implores John—initially introducing himself as "Seán"—to assist in robbing the Mesa Verde National Bank. When John declines, Juan cunningly frames him for the murders of his employer and several soldiers, branding him a wanted criminal. He offers John a dubious protection in exchange for his cooperation, forcing John to reluctantly agree to the robbery. However, seeing an opportunity, John escapes before reaching the bank.
Arriving in the city ahead of Juan, John allies himself with revolutionaries led by the physician Dr. Villega. The pair orchestrates a daring attack on the Mexican army by targeting the bank, but Juan is taken aback to discover that the bank serves not merely as a financial institution, but rather as a prison for political dissidents. In an unexpected turn, Juan emerges from the mission as a celebrated figure among revolutionaries after liberating several prisoners.
However, the tide turns as Colonel Günther Reza leads an army detachment to pursue the revolutionaries into the hills. John and Juan, equipped with explosives, bravely volunteer to stay behind and hold their ground. An explosive battle ensues, causing massive casualties when John detonates a bridge, but Reza survives the encounter. Following the chaos, both John and Juan are devastated to find that many of their comrades, including Juan's family members, have perished due to the army's brutality. Overcome by grief and rage, Juan vows to confront the army single-handedly, leading to his capture.
At this point, John infiltrates the enemy camp where he witnesses a brutal execution of revolutionaries, shockingly revealing Dr. Villega's role in informing on them. This betrayal sparks painful memories for John of his past in Ireland, where his own friend, Nolan, had betrayed him, setting him on a path of violence and exile. Just as Juan faces the firing squad, John intervenes, using dynamite to free him.
The pair successfully escape on a motorcycle, seeking refuge in the animal compartment of a train. Fate has them encounter the tyrannical Governor Don Jaime, who is escaping with his riches. When revolutionary forces ambush the train, John presents Juan with a harrowing choice: kill Jaime or accept a bribe. In an unexpected move, Juan chooses to kill Jaime, seizing his loot. Upon exiting the train, he is triumphantly hailed as a hero once again amidst the revolutionaries.
As they travel with the revolutionary command, John and Juan are rejoined by the escaping Dr. Villega, although only John knows of Villega’s treachery. Faced with a looming threat from Pancho Villa's forces and an impending train packed with enemy soldiers, John devises a bold plan to rig a locomotive with dynamite to thwart their enemy. When it comes time to select a partner for this dangerous mission, John chooses Villega over Juan, despite Juan's eagerness to help. Despite John's pleas for Villega to abandon the train before it crashes, the latter's guilt keeps him aboard. John leaps to safety just in time, while the trains’ collision results in the death of Villega and many Mexican soldiers.
While the initial ambush is successful, John suffers a critical injury from Reza's gunfire during the aftermath. Enraged, Juan retaliates, killing Reza, but as John lays dying, he is haunted by memories of Nolan and a shared love interest. As Juan kneels beside him, seeking information about Villega's fate, John only remarks that Villega "died a hero of the revolution." With Juan rushing to find help, John triggers an explosive charge he secretly planted, obliterating everything. Later, as he watches John's charred remains, Juan reflects despondently on their journey, whispering, “What about me?”
