After a NASA probe crashes in Mexico, alien life forms proliferate across the U.S.-Mexico border, resulting in a quarantine of half of Mexico. Both the U.S. and Mexican military engage in a relentless battle to contain these creatures through airstrikes and defoliation efforts, while a massive wall along the American border is erected to ensure safety. The story begins with gripping night vision footage of a U.S. Army patrol navigating through a deserted town. Suddenly, an explosion rocks one of their vehicles, revealing chaotic flashes of gunfire as soldiers fight back against an enormous, tentacled creature. Amidst this turmoil, a haunting radio transmission seeks clearance for a dangerously close airstrike, while a civilian desperately cries out for help as he tries to rescue a woman from the creature's grasp. In the ensuing chaos, the soldiers retreat, leaving the man behind as he carries the woman away just moments before an air-to-ground missile strikes the beast.
The main narrative unfolds a few days before this ambush, focusing on Andrew, a young American photojournalist working in Mexico. He is tasked by his wealthy employer to escort his daughter, Samantha, back to the U.S. Their initial meeting is awkward, as Andrew, burdened by thoughts of his estranged six-year-old son’s birthday, shows little enthusiasm for being a chaperone. Meanwhile, Samantha grapples with her life choices, her relationship with her father, and her upcoming marriage.
As they attempt to reach the coast for a boat to America, they encounter obstacles when the railway is destroyed and realize that the alien migration season is approaching prematurely. Their window of escape is rapidly closing; if they don’t leave soon, they’ll be trapped for six months. Upon arriving at the port, Andrew is forced to spend $5,000 to secure a ferry ticket for Samantha. That evening, they share drinks and deeply connect, yet when Samantha makes it clear she doesn’t reciprocate Andrew's romantic interest, he drowns his sorrows by sleeping with a local girl. The next morning, when Samantha arrives to say goodbye, she discovers Andrew in bed with someone else and leaves heartbreakingly. Unfortunately, they both discover their passports have been stolen, preventing her from boarding the ferry. Their only option now is to navigate through the perilous "Infected Zone," which will require Samantha to part with her valuable engagement ring as a bribe to pass the checkpoint.
Their journey unfolds across Central America, navigating by boat, where they witness the devastation caused by the aliens, yet also see nature reclaiming the untouched spaces. They travel under the protection of armed guards, encountering the creatures that are reshaping the environment, leading to an intense attack by one such monster. Through these shared experiences, Andrew and Samantha's relationship evolves from mere friendship into something deeper. Eventually, they arrive at the massive wall that divides the Infected Zone from the U.S., only to find that the entire Texas region has been evacuated, and the aliens have advanced significantly into American territory.
As they traverse an evacuation route, they stumble upon an abandoned gas station. Andrew contacts the police, who inform them that they are fortunate to be alive, as an Army rescue unit is nearby. Both Andrew and Samantha reach out to their families—Andrew to his son and Samantha to her father—bringing a sense of reconciliation. Just when things seem dire, an alien appears to threaten them, only for it to be revealed that there are actually two aliens communicating in a non-hostile manner. In a poignant moment, Samantha whispers, "I don't want to go home," prompting a tender kiss between Andrew and Samantha. Their moment is fleeting, interrupted by the arrival of the army, who whisk them away to safety. As the screen fades to black, the narrative cleverly loops back to the opening scene, with the soldiers driving through the deserted road at night, encountering the creature in their path once again.
