At a christening ceremony in a Mexican church, the walls shake and the building collapses when a sudden earthquake strikes. While men clear the rubble, one of the survivors, a 19-year-old Mexican girl named Maria (Elpidia Carrillo), carries her baby and follows her younger brother, Juan (Manuel Viescars), through the wreckage.Meanwhile, in Los Angeles, California, immigration Officer Charlie Smith (Jack Nicholson) arbitrarily arrests two Mexican workers from a factory. Later, Charlie returns to his run-down trailer home where his wife, Marcy (Valerie Perrine), tells him that she wishes to buy a duplex in El Paso, Texas, next door to her friend, Savannah (Shannon Wilcox). Charlie muses over the idea of changing careers and working with park services, but Marcy believes it would be a mistake.As Charlie and Marcy move to El Paso, Maria, Juan, and the baby reach the U.S.-Mexico border. Charlie and Marcy meet Savannah, her husband, Cat (Harvey Keitel), and their young son Timmy (Jay Thurman) at the house. Inside, Savannah and Marcy laugh remembering their days as high school cheerleaders. After Cat has Charlie outfitted for his uniform as a border patrolman, Charlie's new partner, Hawker (Alan Fudge), drives him around the three-mile-long "Tortilla Curtain" border fence, where they encounter a group of young Mexicans sneaking across. Because Hawker identifies them as day workers sneaking into the U.S. for the workday before returning to Mexico at night, he lets them get away.That night, Hawker and Charlie respond to an urgent call, and Hawker is shot and killed by an armed illegal immigrant. The next day at border patrol headquarters, Charlie meets Red (Warren Oates), the patrol supervisor, and attends Hawker's funeral. Later, Charlie walks along the Rio Grande River and becomes transfixed when he spots Maria holding her baby. Charlie returns home to find that, to his annoyance, Marcy purchased a waterbed and opened a charge account at the local mall.In the desert, Cat and Charlie arrest a Mexican man smuggling cocaine and load a group of immigrants into a van to drive them back across the border. Among them, Charlie recognizes Maria, but when he approaches her, she spits in his face. After Charlie locks the drug smuggler in a cell at patrol headquarters, Cat sends the patrol's Mexican contact, Manuel (Mike Gomez), to speak with the criminal.Later, Cat suggests that Charlie participate in his and Red's scheme; smuggling immigrants for extra money, but Charlie refuses. At home, Marcy tells her husband that she wants to work on television and he discovers that she installed a swimming pool. At the Rio Grande river border, Charlie calls out to a woman he believes to be Maria, but is mistaken. He crosses the water into Mexico and walks through a poor village, where he finds the drug smuggling boy with his throat slit.Back in Texas at Red's birthday party, Charlie tells Cat and Red about the body, suspecting Manuel of suspicious dealings. Cat dismisses the idea and Red banishes Charlie from crossing the border again. One night, Charlie and Cat attempt to stop a group of Mexicans, including Maria and her brother, from hopping onto a freight train. When Juan falls under the train, Charlie jumps under the train to protect him.While detained in an outdoor holding cell, a woman offers to hold Maria's child and scuttles off to hand the baby to Manuel. Maria realizes the baby is gone and begins to cry, prompting an uprising from the other detainees, who break out of their cage. The patrolmen use tear gas to control the crowd and load the detainees on a bus to drive them back to Mexico.That night, Cat confronts Manuel about the stolen baby and Manuel reveals that he sold the child to a wealthy Caucasian family. As they talk, they see El Scorcho, a man with a burned face who traffics Mexicans in competition with their own arrangement. Charlie wakes up the next morning to the sounds of Marcy moving more furniture into the house. Fed up with her excessive spending to build him the perfect "dream house," he slaps her. Charlie and Cat visit J. J. (Jeff Morris), whose house acts as a delivery station for smuggled immigrants. As Charlie waits outside, J. J. hands Cat a stack of money.During a pool party at the Smiths' house, Savannah drunkenly starts a food fight, prompting Marcy to scream. Amidst the chaos, Charlie dumps a grill full of burning meat into the pool.One afternoon, Charlie catches El Scorcho with a truckload of Mexicans. Cat suddenly arrives and takes El Scorcho back toward the station, but Jack hears two gunshots from the direction in which Cat drove away. At the station, Charlie yells at Cat that he does not want to get involved with murder. Marcy gets her hair done at the salon and worriedly tells Savannah that she does not know how to make Charlie happy.Outside a bar another night later, Charlie pays Juan $5 to take him to Maria and finds her in a strip club, where she works as a dancer for Manuel. When he tries to lead her away, two men beat Charlie up and throw him outside.The next day, Manuel warns Cat that Charlie will get them into trouble. As Charlie chases a driver through the desert, he fails to notice two Mexicans who are being transported. Cat watches the incident from a distance. When the driver confesses to transporting two men, Charlie returns to the site to check again. Inside the driver's vehicle, he finds their bloody bodies, which he swears had not been there before. Cat insists he will cover for Charlie and they sink the car in a nearby pond. Charlie again asks Juan to take him to see Maria and informs them that he will help smuggle them across the border the next day. He insists that she does not owe him anything, and that helping them would allow him to feel good about something in his life.The next night, Charlie watches as Maria, Juan, and a group of others safely cross the Rio Grande. Outside J. J.'s house, Maria's group boards a truck and Charlie and Cat take their payment for the delivery. However, Juan is shot for attempting to smuggle drugs, and he runs away. Two patrolmen notice the truck on the highway and follow in pursuit. Charlie hears the call on his patrol radio and, concerned about Maria, drives to catch up with them. Gaining speed, the truck loses control and crashes on a hillside. Charlie takes Maria home and asks Marcy to tend to the girl while he returns to J. J.'s house to look for Juan. Once there, he overhears Red talking with J. J., explaining how the heist went wrong. Charlie returns home to take Maria back to Mexico, but Marcy believes he is leaving her. Although he and Maria find Juan, bloody and feverish, he dies shortly after. As Maria prays over her brother's body, Manuel and J. J. prowl outside and Charlie shoots J. J. in the face. Charlie finds Manuel at a bar and demands he return the baby, who has not yet been sold, to Maria.At the house where the baby is hidden, Charlie finds the infant buried in a laundry basket, and Manuel calls the patrolmen. On the road, Cat and a few other officers shoot at Charlie as he drives by. Charlie gets out of his vehicle and fires at the officers, exploding their car, and Cat hides under a bulldozer. Charlie shoots the tire, which deflates and causes the oversize vehicle to crush Cat to death. Charlie returns to the Rio Grande crossing and delivers the baby to Maria, who thanks him through her tears.