Dr. Miles Bennell, a physician in the small town of Santa Mira, California, begins receiving panicked visits from patients claiming their loved ones are being replaced by emotionless impostors. Initially skeptical, Miles is eventually convinced something is amiss when he himself witnesses a partially formed duplicate of a close friend. His colleague, Dr. Dan Kauffman, a psychiatrist, dismisses the phenomena as mass hysteria, but the uncanny occurrences continue to escalate. With the help of his former girlfriend Becky Driscoll, Miles starts to uncover a chilling truth.

As Miles and Becky dig deeper, they discover mysterious pods that seemingly produce replicas of townspeople while they sleep. The duplicates are perfect physical copies but devoid of human emotion. With paranoia mounting, Miles and Becky must navigate a labyrinth of suspicion and dread, trying to alert authorities and find allies before they too fall victim to the alien menace. Their journey takes on an urgent pace as the once-familiar community becomes increasingly unrecognizable, and they find themselves alone in their fight against an insidious threat that grows stronger with each passing moment.