After a space shuttle disintegrates on re-entry, scattering debris across the U.S., a seemingly benign alien virus arrives on Earth. This virus quickly begins to alter the behavior of those it infects. Carol Bennell, a Washington, D.C. psychiatrist, starts to notice subtle changes in the people around her, including her patients and her ex-husband. These infected individuals soon display a frightening level of emotional detachment and conformity. Carol's initial skepticism turns to concern, and then to terror, as she realizes the scale of the infection.

Desperate to find her son, Oliver, who is in the custody of her infected ex-husband, Carol teams up with her friend Ben Driscoll, a fellow doctor. Together, they seek to understand the nature of the virus and how it spreads, discovering its frightening efficiency at taking over human hosts during their vulnerable sleep. As society begins to crumble around them, and with the infected now in positions of power attempting to spread the virus further, Carol and Ben must stay awake long enough to find a way to save her son and, hopefully, humanity itself from an emotionless and conformist future.