At a solemn christening ceremony held in a quaint Mexican church, chaos erupts when an unexpected earthquake violently shakes the building, leading to its devastating collapse. Amidst the tragic rubble, Maria, a resilient 19-year-old girl portrayed by Elpidia Carrillo, clutches her infant and desperately follows her younger brother Juan (Manuel Viescas), navigating through the destruction to safety.
Meanwhile, in the bustling city of Los Angeles, California, immigration officer Charlie Smith played by Jack Nicholson finds himself caught in the morally gray waters of law enforcement as he arbitrarily detains two Mexican factory workers. Later, he returns to his dilapidated trailer home where his wife Marcy (Valerie Perrine) expresses her desire to buy a duplex in El Paso, Texas, next door to her friend Savannah (Shannon Wilcox). As the couple discusses their future, Charlie dreams of a possible career shift to park services; however, Marcy cautions him against abandoning his current job.
The story progresses as Charlie and Marcy embark on their move to El Paso, while Maria, Juan, and the baby reach the turbulent U.S.-Mexico border. The couple soon becomes acquainted with Savannah, her husband Cat (Harvey Keitel), and their young son Timmy (Jay Thurman) upon arriving at their new home. Inside, moments of laughter and nostalgia bloom as Savannah and Marcy reminisce about their high school days as cheerleaders. The atmosphere shifts when Cat outfits Charlie for his new position as a border patrolman. His new partner Hawker (Alan Fudge) introduces him to the grueling realities of the "Tortilla Curtain" border, where the duo comes across several young Mexicans attempting to sneak into the U.S. for a day’s work. Though Hawker recognizes them as day laborers and allows them to escape, the tension of the border doesn’t dissipate.
As night falls, the fragile peace is shattered when Hawker is tragically shot and killed in a confrontation with an armed illegal immigrant. This event catalyzes Charlie's encounter with Red (Warren Oates), the patrol supervisor, at Hawker's funeral. Deeply troubled, Charlie takes a solitary stroll along the Rio Grande River, where he unexpectedly spots Maria cradling her baby, igniting a mixture of empathy and frustration in him. Returning home, he's greeted by Marcy's latest impulsive purchase: a lavish waterbed, escalating his annoyance over their strained finances.
The plot thickens in the unforgiving desert when Charlie and Cat apprehend a Mexican man involved in cocaine smuggling. During their ordeal, Charlie recognizes Maria among those being loaded into a van. However, when he approaches her, she retaliates by spitting in his face. After subduing the drug smuggler and locking him at the patrol headquarters, Cat proposes a morally dubious side venture: to profit by smuggling immigrants. Charlie declines the offer firmly, further complicating his marital struggles when Marcy reveals her aspiration to break into television, coupled with yet another extravagant home improvement—the installation of a swimming pool.
In his relentless pursuit of understanding and redemption, Charlie embarks on another reckless mission across the Rio Grande, believing he saw Maria. His search leads him through a destitute Mexican village, where the haunting discovery of a boy's body serves as a grim reminder of the dangers lurking at every corner. During a gathering for Red's birthday, during which Charlie voices suspicions regarding the local contact, Manuel (Mike Gomez), he finds himself ostracized after being warned not to cross the border again.
In a series of harrowing events, Charlie becomes embroiled in a violent encounter with Cat and a group of Mexicans, including Maria and Juan, resulting in Juan's tragic fate when he falls under the freight train's merciless wheels. The emotional turmoil reaches a crescendo as Maria's child is taken amidst the chaos of an uprising among the detainees. Although their immediate plight is quelled by law enforcement's tear gas confrontation, the harsh reality of the situation sends ripples through Charlie, leading him to confront the nefarious El Scorcho, who competes with their smuggling operation.
As tensions build, accidental shootings intertwine with Charlie's intentions, revealing his internal conflict. He eventually finds himself in a gritty showdown with Cat and Red, leading to bloodshed, further implicating him in a web of violence and moral ambiguity. The climax reaches a fever pitch when Charlie delivers Maria's baby back to her after an intense chase, where he takes on not just the complications of border patrol but also the monsters that lurk in the shadows of power and desperation.
This heart-wrenching tale encapsulates not merely the experience of immigration and survival, but also examines the profound moral dilemmas faced by individuals caught between duty and empathy. As Maria sheds tears of gratitude upon receiving her child, the story reflects on the choices made in the name of humanity amidst chaos and tragedy.
