Marti Malone, a rebellious teenager, moves with her family to a military base in Alabama where her father, Steve, has been assigned to conduct an environmental study. As they settle in, Marti befriends the troubled daughter of the base commander, who hints at strange occurrences among the personnel. Marti's stepmother begins acting oddly, raising Marti's suspicions. What seems to be a standard military environment quickly turns eerie as Marti notices an increasing number of people behaving in odd and emotionless ways. Her father uncovers a toxic waste hazard in the river, but the real threat is something far more terrifying.

As Marti digs deeper, she discovers that the base has become ground zero for an alien invasion. Parasitic pod-like creatures are replacing humans with soulless duplicates as they sleep, erasing emotions and individuality. With trust in short supply and her family's safety on the line, Marti must navigate a landscape where anyone could be an imposter. She teams up with fellow survivors to fight back against the rapidly spreading menace, racing against time to both save her family and alert the outside world.