In August 1994, at the Tarasco bar in Mexico, an American named Buscemi recounts a harrowing tale of a massacre he witnessed in another bar, carried out by a Mexican armed with a guitar case filled with guns. The crowd initially pays him little heed until he utters the name "Bucho." At the same time, El Mariachi, played by Antonio Banderas, experiences a haunting dream involving Moco, Bucho’s ruthless subordinate, who killed his lover and injured his left hand. Buscemi wakes him from this troubled slumber, pushing him to pursue Bucho at the bar, where the mere mention of the name sent shivers through the patrons.
As El Mariachi traverses the streets, he meets a child whose father purportedly makes a living by playing guitar, offering him some advice. Yet, the escalating tension at the Tarasco bar culminates in a raging gunfight, where El Mariachi subdues Bucho's henchmen, leaving a path of destruction in his wake. However, Tavo—who had been hiding in a back room—sustains a wound to El Mariachi before meeting his end in a confrontation. In a moment of vulnerability, Carolina, portrayed by Salma Hayek, saves El Mariachi from further harm and takes him to her bookstore, where their fates intertwine.
As chaos unfolds, Bucho inspects the aftermath of the bar's devastation, his paranoia palpable due to the Colombian cartel’s scrutiny over his operations. Desiring everything to be flawless, he orders his men to track down the "man dressed in black." Within the sanctuary of Carolina's bookstore, she tends to El Mariachi's wounds and uncovers his true identity when she discovers the armed machine hidden within his guitar case. Their shared journey deepens as El Mariachi implores her to aid him in finding Bucho.
Confrontations escalate when a shadowy figure, also garbed in black, ambushes them outside the church, leading to another tragedy with the murder of Buscemi and inflicting further injury on El Mariachi. Mistaking this attacker for El Mariachi, Bucho's men erroneously eliminate a hitman sent by the Colombians. As El Mariachi wanders through the town's streets, he learns from the lad about the grim reality that many are enslaved to Bucho’s narcotics trade, including Carolina herself, who unwittingly has links to his drug empire.
This revelation evokes a profound sense of urgency as El Mariachi confronts Carolina, discovering that for Bucho, her bookstore serves as yet another front for his illicit dealings. The tension rises further when Bucho pays her an unexpected visit. As their connection becomes undeniable, the couple shares a passionate night together, but the dawn brings danger as Bucho’s men attack, setting the bookstore ablaze.
As they escape the inferno, El Mariachi finds himself with a rare opportunity to take out Bucho, yet he hesitates, choosing instead to seek refuge in a hotel room. Determined to end the relentless pursuit, El Mariachi calls upon his allies, Campa and Quino, for assistance. Together, they engage in a fierce battle against Bucho’s crew, suffering great losses as they emerge battered but resolute to further seek justice for their fallen friends.
Ultimately, El Mariachi and Carolina make their stand at Bucho's stronghold, where the truth unfolds: Bucho and El Mariachi are, in fact, brothers. In a heart-wrenching twist, El Mariachi is faced with an impossible choice as Bucho offers him a bargain—his own life in exchange for Carolina's. In a moment steeped in anguish, El Mariachi confronts his brother, leading to a tragic conclusion where he eliminates Bucho and the remaining henchmen.
Their journey does not end in despair; rather, they tend to the wounded child in the hospital, showcasing their enduring nobility. While El Mariachi initially walks away from his past, Carolina catches up to him, and together they embark on a new chapter, momentarily leaving behind the guitar case filled with weapons, only to reconsider and return for it—prepared for whatever the future may hold.
