一艘太空船在华盛顿附近的小镇坠毁,人们一觉醒来,发现身边的人变得冷漠而陌生。精神科医生卡罗尔(妮可•基德曼 饰)和助手本(丹尼尔•奎格 饰)几经周折,发现这种变化是因为感染了外星病毒。灾难不可控制的蔓延,感染的人越来越多,他们占领城市,设置隔离区,想把人类变成没有情感的怪物,卡罗尔带着儿子奥利弗开始逃亡,她惊奇地发现奥利弗正是拯救人类的希望。While returning to Earth, the space shuttle explodes and the fragments bring an alien virus that recodes the human DNA. In Washington, the psychiatrist Carol Bennell observes the modification of the behavior of one of her clients first, then in her former husband and finally in the population in general. Together with her friend Dr. Ben Driscoll the researcher Dr. Stephen Galeano, they discover that the extraterrestrial epidemic affects human beings while sleeping and that her son Ollie, who had chickenpox when he was a baby, is immune to the disease and may save mankind from the outbreak.