The story begins with a gripping scene where a desperate man hastily fills bags with cash as night falls, leaving a lifeless body in an office behind him. Soon, his reckoning arrives as a vengeful mob, fueled by anger, descends upon him, delivering a gruesome retribution with a machete.
With the chaos settling, it becomes apparent that the victim was the mayor of San Pedro de los Saguaros. In an effort to evade scrutiny ahead of the 1952 general elections, State Governor Sánchez orders Secretary López to seek a temporary replacement. López assigns the task to Ramírez, who suggests Juan Vargas, the ostensibly innocent head of a local landfill, for the position.
Overjoyed by this unforeseen opportunity, Vargas, alongside his wife Gloria, initially basks in their newfound fortune. However, their excitement quickly dims as they arrive in a San Pedro riddled with poverty and ignorance. Most residents, unable to articulate their frustrations in Spanish, remain silent observers of their hardships.
Despite Gloria's concerns, Vargas opts to stay in San Pedro and investigate the potential this new role offers. Under the guidance of his secretary Carlos Pek, he uncovers a history of corruption that has tainted previous administrations, meeting pivotal characters along the way, such as Doña Lupe, the mystifying owner of the town's brothel; the selfish Parish Priest Pérez; and Doctor Morales, a learned member of the opposition PAN.
As Vargas grapples with an empty municipal budget due to prior mismanagement, he travels to the state capital in hopes of appealing to López for additional funds. Unfortunately, his journey takes an unexpected turn when his car breaks down, leading him to encounter Robert Smith, an American who offers to pay him for services while using an alias. Though Vargas receives a copy of the Mexican Constitution and a revolver during a setback encounter with López, he feels undeterred.
As Vargas immerses himself in the intricacies of governance, he stumbles upon numerous constitutional loopholes ripe for exploitation, thereby extracting fines and taxes from those who dare challenge him. His initial attempts to shut down the scandalous brothel face resistance from Doña Lupe, who threatens him with a cleaver, sending Vargas fleeing in terror. This confrontation leaves him both shaken and motivated by the lure of financial gain. Later, when Doña Lupe proposes a profitable arrangement in exchange for his complicity in her illicit dealings, Vargas decides to give in to temptation, thereby paving the way for his impending corruption.
As time passes, Vargas's moral decline accelerates. He weaves an intricate web of lies and manipulates the law, imposing harsh taxes that burden the townspeople. To improve his standing, he introduces Robert Smith, an engineer tasked with modernizing the town through electric lighting, presenting it as a 50-50 partnership that coincidentally allows Vargas to accommodate Smith in his home.
Meanwhile, Doña Lupe's tolerance wanes as Vargas's requests for payment and favors grow increasingly outrageous. In retaliation, she hires a menacing enforcer who viciously assaults Vargas during a debt collection effort. Fueled by rage, Vargas seeks revenge that same night, ambushing both the enforcer and Doña Lupe, brutally killing them and disposing of their remains in a ravine. Unknown to him, he leaves behind his PRI pin, a damning clue of his involvement.
Upon realizing his pin is missing, Vargas panics and instructs Pek to launch an investigation to buy time. To divert suspicion from himself, he frames Filemón, the town's notorious drunkard, as the perpetrator, with Doctor Morales falsely claimed to be the mastermind. Morales is subsequently exiled, facing accusations related to local women.
During Vargas's journey to jail with "Filemón," he discovers the drunkard has found his pin near the ravine. Despite an earlier plan to bribe him with cash and liquor, Vargas heartlessly murders Filemón and discards his body by the roadside.
Returning home, Vargas is faced with a staggering piece of news: his wife has betrayed him with Smith. Enraged and hurt, he loses control, tying Gloria up and brutally assaulting her. This act sets the stage for his tyrannical rule, where he enforces draconian taxes and harsh penalties upon the townsfolk. Pek, horrified by Vargas's conduct, declares him "the worst municipal president this town has ever known," as fear grips the once-peaceful community.
Simultaneously, López arrives in town, looking for retribution after a failed attempt on a political rival, demanding Vargas relinquish the profits he accrued. In a confrontation at Vargas's home, he learns that Gloria has escaped to the United States with Smith, taking all their wealth with her. This triggers a downward spiral for Vargas, who, in a frenzy, kills López and his henchman Tiburón before facing an angry mob led by Father Pérez and Pek.
Just as Vargas's fate seems sealed at the hands of the mob, government officials arrive, chasing López and intervening just in time to rescue Vargas from certain death. In the aftermath, he manages to reinvent himself, portraying himself as the hero who brought justice to corrupt López. Ramírez finds comfort in his new position as the administrator at the landfill where Vargas once toiled. As a new mayor makes his entrance into San Pedro de los Saguaros, it becomes unmistakably clear that history is destined to repeat itself – echoing the very circumstances that brought Vargas and Gloria to this troubled town.
