Peter, an engineer portrayed by Michael Peña, grapples with haunting nightmares that strain both his mind and family life, as they depict intense encounters with an unknown alien adversary. As these visions escalate in intensity, they start impacting his wife, Alice Caplan, who implores him to seek professional help. At work, Peter’s episodes further disrupt his life, leading to serious workplace incidents. Concerned for his well-being, his boss, David, recommends he visit a specialized clinic.
After a particularly harrowing episode that results in him blacking out for hours, Peter reluctantly agrees to the intervention. At the clinic, he encounters Chris, a fellow patient who shares troubling visions of his own. Chris reassures Peter that he isn’t losing his mind and encourages him to trust his visions—an idea that has driven Chris to consider erasing his memories through treatment. However, motivated by Chris’ insights, Peter decides to exit the clinic without seeking further help.
Later that day, as Alice throws a celebration for her recent promotion at an architecture firm, Peter becomes increasingly consumed by the anomalies plaguing his mind. While guests mingle, he fixates on the sky, desperately searching for evidence of an alien incursion. Meanwhile, their friends and neighbors, Ray and Samantha, offer support to Alice amidst the chaos. Just as Ray attempts to interject with logic, Peter spots ominous lights in the sky. Suddenly, invading spacecraft unleash devastation on the city, impacting their apartment building.
Amidst the ensuing turmoil, Peter and Alice realize their daughter Hannah is missing. When Ray discovers his daughter Megan is also unaccounted for, the two men understand the children may have gone off together. They rush to find the girls, but upon rescuing them from an elevator, they uncover a grave situation: alien ground troops are infiltrating their building and executing people.
As the families take shelter, Peter and Alice barricade themselves while the children cower in fear. When a soldier attempts to breach the door, Peter and Alice strain to keep it shut. Distressed from the unfolding chaos, Lucy, played by Erica Tremblay, leaves her hiding spot for her precious stuffed monkey, Herman. In a moment of horror, the soldier breaks a wall, gaining access to the room.
In an intense showdown, Peter ambushes the intruder. Although he wrests control of the soldier’s weapon, a biometric lock prevents him from firing it. In a dramatic turn, Alice uses the telescope—an object meant for stargazing—to incapacitate their assailant. The family makes a daring escape to the building's rooftop and reunites with Ray, Samantha, and Megan, only to witness another horrific scene as a spaceship obliterates a group of survivors trying to signal for help.
Faced with the urgency of the situation, Peter’s group decides they must leave their apartment or risk being killed. They attempt to descend the building via a malfunctioning window-washing lift but are forced back inside just before it crashes.
With a grim realization that a solid refuge awaits in his workplace, Peter recalls that it was designed to withstand assaults. Alice and Samantha propose navigating the city’s underground tunnels to reach the factory. Unfortunately, tragedy strikes when a spaceship attacks, resulting in the deaths of Ray, Samantha, and Megan. Peter’s family escapes onto the building's exterior but are soon pinned down by alien soldiers.
Just in time, Peter bypasses the rifle’s security, enabling them to fight their way to the tunnels, although Alice sustains serious injuries. The soldier from their apartment regains consciousness and tracks them to the underground. A fierce confrontation ensues, but Peter emerges victorious, subsequently discovering that the soldier is human and fluent in English. In disbelief, Peter compels him to assist with Alice’s urgent need for medical help.
As they reach the factory, Miles, the soldier, explains the long-anticipated invasion had been predicted for decades. A medic examines Alice but cannot save her, and in a desperate plea, Miles reveals that Alice is not human but an android. Peter, faced with the dauting task of saving Alice, realizes that he must provide the power she needs—his own lifeforce.
In a moment of courage, Peter preps to sacrifice himself and in an unexpected twist, feels no pain as he pierces his chest. With help from Miles, he manages to save Alice. Upon regaining consciousness, Peter experiences visions of a future where he and Alice navigate a world intertwined with synthetic beings—creations increasingly resembling humans.
As societal tensions arise around the existence of these "synths," Peter and Alice pick up the pieces of their world while raising their daughters. They come to understand their memories had been blissfully suppressed to alleviate the burden of their past actions. While conversing with Miles, Peter learns that humanity had inhabited Mars for several generations, unearthing knowledge about synths with the intent of reclaiming Earth.
As the humans launch their invasion, the synths prepare for battle, leading to a climactic showdown in the factory. Amidst the chaos, Peter proposes a future of camaraderie between humans and synths. Their escape train departs just as the conflict intensifies, providing a brief window to glimpse the ravaged city above before descending into the safety of the underground.
