Delaney Mossbacher is a left-leaning nature writer who lives a comfortable life in affluent style with his wife Kyra, a hard-working realtor. One day Delaney hits an illegal Mexican immigrant with his car. He never learns the Mexican's name, which is Candidó. The accident occurs when Candidó darts without caution into a busy street. Delaney tries to talk to Candidó, but the pedestrian only speaks Spanish and Delaney does not know Spanish. Delaney gives Candidó a twenty-dollar bill, and the badly injured Mexican hobbles off to his campsite, located off a nearby nature trail. Delaney realizes that Candidó must be living in the Topanga State Park, and he grows angry thinking of the fire hazard this illegal alien poses to the park.

In the collision with Delaney's car, Candidó has suffered a concussion. His left cheekbone is crushed, and an arm and a hip give him terrible pain. His wife, América, tries to nurse him back to health. América is seventeen and pregnant, and she has never worked for money. Candidó and América have been living in the park because robbers stole all their savings shortly after they crossed the border into the United States. Several days after being hit by Delaney's car, Candidó's fever breaks, but his injuries prevent him from seeking a laboring job. América goes to the labor exchange, a flimsy outdoor shelter where Mexicans look for day labor, in search of housekeeping work.

Delaney and Kyra have two dogs and a cat. They suffer a trauma when a coyote jumps over their backyard fence and kills one of the dogs, Schaverell. That evening, Delaney attends a meeting at the community center for Arroyo Blanco Estates, the exclusive neighborhood where he lives. The special meeting has been held to discuss a proposed gate, which will keep poor people and illegal immigrants out of their neighborhood. Delaney chastises his neighbors for trying to keep Mexicans out while inviting coyotes in by leaving food and trash in their yards. The meeting is led by Jack Jardine, Delaney's friend and lawyer. Jack has advised Delaney to avoid making an official report about his collision with Candidó. After the meeting, Jack's teenage son, Jack Jr., asks Delaney where he thinks the Mexican has set up camp. The next day, Jack Jr. destroys Candidó's humble camp.

Although he remains too sick to work, Candidó becomes angry when América goes up to the labor exchange and sits with the Mexican men who are looking for work. He worries for América's safety and feels guilty that he cannot provide for her. On her fifth day at the labor exchange, América gets hired by a fat white man to scrub Buddha statues. She works very hard, and the scouring solution burns her hands and throat.

Scared by the destruction of his campsite, Candidó sets up a new camp on a small sandbar beside a small dirty creek. There he builds a shelter from items that people have discarded. Since Candidó has no way of knowing that América has found work, he grows worried when she does not return to the lower canyon by late afternoon. He walks up the path to find her, and along the way encounters an aggressive light-skinned Mexican wearing a backward Padres cap. Along the road that separates the upper canyon from the lower canyon, Candidó searches for América in a supermarket parking lot. Instead he sees Delaney, Jack Jardine, and Jack Jr. Candidó recognizes Jack Jr. as the boy who destroyed his camp, and he believes that Jack Jr. is Delaney's son.

Delaney takes a hike into the lower canyon. Along the path, he runs into the man in the Padres cap and his darker-skinned friend. Delaney feels threatened by the men, and he is angry because he thinks that they have been camping in the park, threatening the natural environment. He cuts his hike short. When he returns to his parking space, Delaney finds that his car has been stolen.

The next day, América and Candidó go to the labor exchange together. When the fat man pulls up, América goes with him to polish statues again, even though he underpaid her and touched her inappropriately the first time she worked for him. Her workday passes without incident. At the end of the day, she looks for Candidó at the supermarket but does not see him, so she heads back to their new campsite alone. On the trail, she encounters the man in the Padres hat and his friend. They rape América.

Kyra hires a contractor to build a backyard fence to keep out coyotes. She notices that one of the workers on the contractor's crew looks like the man Delaney said he hit with the car. Kyra goes to the Da Ros mansion, a real estate listing that is her personal favorite, to lock it up at the end of the day. There she encounters the man with the Padres hat and his poncho-wearing friend. They seem to have been camping on the property's lawn. Kyra tells them to leave and pretends that she lives in the house and has a husband inside. She decides that she will never again go to the Da Ros estate without making a phone call to her secretary.

Candidó returns to the campsite after working on Kyra's fence and sees that América has been attacked. She denies that her attack was sexual, but he knows the truth. He vows that if he ever sees the man in the Padres hat again he will kill him. After being raped, América feels a burning sensation whenever she urinates. She thinks that the burning is perhaps a normal pregnancy side effect, but she wishes that she could discuss it with her mother in Mexico.

Delaney attends a gathering of neighborhood men at the home of Dominic Flood. Flood, a client of Jack Jardine's, is under house arrest for banking crimes. At the gathering, men discuss the need for a tall wall to be built around all of Arroyo Blanco Estates. They believe that a wall will keep them safer from criminals. Delaney disagrees with the other men about the fence. One evening shortly after the meeting, Delaney, Kyra, and Jordan are enjoying their backyard when a coyote climbs over the new fence and takes Osbert, their remaining pet dog.

For weeks, Candidó has been occasionally successful at finding day labor. He has saved several hundred dollars toward first and last month's rent for an apartment. One day Candidó goes to the labor exchange and finds that the shelter has been torn down and a "NO TRESPASSING" sign is in its place. He decides that he must go to Canoga Park, a nearby town that has a large Mexican population, to look for work. América demands that he take her with him. They walk all the way to Canoga Park and enjoy a small meal at a diner there. Then Candidó gets mugged, losing all the money he has managed to save. He and América walk back to the canyon, and he finds food for them in the dumpster behind a fast food restaurant. América is furious and disappointed, and she refuses to do anything but sit before the campfire for weeks afterward.

One night, Kyra locks up the Da Ros mansion and finds a hateful message spray-painted on the back of the house for her. After that, Delaney goes with her to the Da Ros estate each evening. To thank him, Kyra buys Delaney a metal ladder to climb over the backyard fence.

Kyra and Delaney have had a falling out over the issue of the community fence. She favors the fence idea because she thinks that it will keep out coyotes. Outside the Arroyo Blanco Estates community center, Delaney overhears Jack Jr. and a teenage friend discussing Mexicans in a hateful way. Walking alone, Delaney sees the man in the Padres hat and thinks that he is the man Kyra described seeing at the Da Ros estate. Delaney confronts the man but backs down when he sees that the man in the hat is doing work, delivering fliers that have a pro-fence message.

Candidó finds occasional work with an elderly, alcoholic building contractor. On the night before Thanksgiving, Candidó goes to the grocery store and someone gives him a free frozen turkey. He brings the turkey to América, and her spirits are lifted.

On Thanksgiving Day, Delaney and Kyra interrupt their meal preparations to attend an elegant party at Dominick Flood's house. They bring with them Kyra's mother, Kit, who is charmed by Flood. Suddenly, an announcement that fire has broken out it the lower canyon interrupts Flood's party.

Down in the canyon, Candidó has accidentally started a fire by lighting a match to cook the turkey. He and América run desperately up the hillside. By the time they make their way up to the upper canyon, Arroyo Blanco Estates residents have evacuated their homes. Candidó takes América to a gardener's shed that interrupts the community's wall, and she gives birth there. A cat enters the shed and provides comfort to América during the delivery.

The residents of Arroyo Blanco Estates wait behind a police barricade on a road outside the neighborhood. When two Mexicans—the man in the Padres hat and the man in the poncho—appear, Delaney and several others ask the police to arrest them for starting the fire. Delaney gets into a physical brawl with the man in the hat. Later, Delaney and his family return home to find that their cat, Dame Edna, is missing. Kit is embarrassed to find Dominick Flood's ankle monitor in her purse, and she realizes that he has used the fire as an opportunity to escape and flee the country.

América gives birth to a baby girl and names her "Socorro." Candidó climbs over the fence and steals supplies from the backyards of Arroyo Blanco Estates. Using discarded wood pallets and the unattached roof of a gardener's greenhouse, Candidó builds a structure for his family in the brush outside the wall. He kills Dame Edna for stew.

Delaney realizes that he has come to hate Mexicans. After some Hispanic-looking graffiti appears on the gate to Arroyo Blanco Estates, he sets up a trap of cameras and trip wires to catch the culprit. One night his cameras catch Candidó, and Delaney recognizes him from the auto accident.

América tells Candidó that she wants to go back to Mexico. She wants to show Socorro to her family. Candidó wishes that he could afford to put América and the baby on a bus, but the fire has burned their savings. América notices that Socorro appears to be blind.

After a long day of standing outside the post office in the hope that someone will hire him to do manual labor, Candidó steps onto the street and sees Delaney's Acura. Delaney furiously chases Candidó with his car, causing a collision with another vehicle. Delaney deserts his car and chases Candidó up the hillside and tracks him to his shack.

Rain comes down heavily. Delaney goes home to put on a rain jacket and get his gun. He develops some photos taken by his camera trap, and discovers that Jack Jr. is the culprit behind the graffiti. Knowing this, Delaney still feels hatred toward Candidó. Delaney destroys the photos and sets off to confront the Mexican.

At the moment when Delaney opens the door to Candidó's shack, the shack gets caught in a mudslide. Candidó tries to hold onto América and Socorro, but the baby gets lost in the mud. Candidó sees Delaney trapped in the slide, and he offers Delaney a hand to help him.