Marti Malone, portrayed by Gabrielle Anwar, is a teenager who feels estranged from her father, a newly remarried Environmental Protection Agency agent played by Terry Kinney, and her stepmother, Meg Tilly, as well as her young brother, Andy. The family's journey begins at a remote military base, where Marti's father has been assigned to investigate potential contaminants linked to a recent outbreak of mass hysteria amongst the personnel. On the way, they stop at a quaint rural gas station, where Marti encounters a frantic serviceman who ominously warns her, stating, “they are everywhere.” When she rushes to inform her father, the mysterious figure has vanished.
Once the family arrives at the base, Marti attempts to navigate her new surroundings by befriending the commander's rebellious daughter and flirting with the handsome attack helicopter pilot, Tim Young, played by Billy Wirth. Meanwhile, Marti's father begins to engage with Major Collins, portrayed by Forest Whitaker, who raises alarms about narcophobia—the fear of sleep—while noting an alarming increase in paranoia among the base's inhabitants. Initially dismissive, Marti's father soon realizes the seriousness of the situation after discovering dangerously high toxicity levels and bizarre mutant plant life.
As night falls, Marti witnesses a horrifying transformation; her stepmother crumbles to dust, revealing a soulless pod duplicate. The pod-woman tries to persuade Marti's father of the benefits of the invasion, claiming it will eradicate confusion and anger. Although on the verge of succumbing to her manipulative words, his children arrive just in time to pull him away, triggering a terrifying alarm from the pod-female as she raises an echoing, unnatural scream.
From this point, the narrative intensifies as Marti, her father, and Andy find themselves pursued by pod-people across the base. They soon encounter a handful of other remaining humans who join their frantic escape. As searchlights blaze overhead, the terrifying sight of the pod clones overtaking the base unfolds. Marti and Andy take refuge in a warehouse laden with barrels of toxic waste while their father sets off to seek help. He breaks into Major Collins' office, where he finds the Major overwhelmed and desperate, turning to sleep-prevention pills for solace. Their conversation is swiftly interrupted by the relentless arrival of the pod-people, led by the base commander. Faced with the prospect of losing his individuality, the Major chooses to end his life rather than live in a world devoid of humanity.
Marti's father swiftly returns to find Marti and Andy, claiming he's discovered a potential escape route. As they drive through the chaotic base, loudspeakers urge the residents to facilitate the invasion by transporting pods in trucks. Marti's increasing unease prompts her to question their destination, but her father's vague reassurances only heighten her suspicions. Realizing that he has been podded while he was away, Marti swerves the vehicle in a desperate attempt to flee with her brother. They are soon confronted by Tim, who is still oblivious to the unfolding danger. In a shocking turn of events, Marti reluctantly shoots her pod-father, watching in horror as he transforms into a grotesque, bloody mass.
Seeking safety, Marti, Tim, and Andy hide in a nearby hangar. Tim decides to venture out alone to avoid detection, disguising himself as a pod-man when confronted by enemies. Meanwhile, he keeps a watchful eye on Marti and Andy as the pod-people close in. Just as Marti is on the brink of being taken over by her pod clone, Tim swoops in to revive her. After escaping the building, they try to maintain a facade of emotionlessness to reach Tim's helicopter. However, their plan crumbles when the commander's daughter becomes suspicious, leading to a frantic chase. Just as they are about to take off, Andy attacks Tim, forcing Marti to make the heart-wrenching decision to throw her controlled brother from the helicopter.
As dawn breaks, Marti and Tim launch a daring assault on the base using the helicopter's weaponry, destroying the pod-making facility and obliterating many of the clones. In the film's chilling final moments, as Marti and Tim escape in their helicopter, they ponder the ambiguous fate of humanity. The haunting words of Marti's infected stepmother come to mind, constituting a grim reminder of the ever-looming threat: “Where are you gonna go, where are you gonna run, where are you gonna hide? Nowhere... 'cause there's no one like you left.”
