The employee of the Department of Public Health, Elizabeth Driscoll, tells his friend and coworker, the field investigator Matthew Bennell, that her boyfriend Dr. Geoffrey Howell is not the same person - he is behaving differently. Matthew suggests that Elizabeth pays a visit to his friend, the renowned Dr. David Kibner. They meet him in a lecture and he tries to convince her that she has some emotional problem with Geoffrey, while Elizabeth notes that other people are having the same complaint. When Matthew's friends, Nancy and Jack Bellicec, find a clone of Jack in their medical mud business, they call Matthew and he immediately seeks out Elizabeth. He breaks in her house and finds a clone of her. The quartet discovers that people are being replaced by exact emotionless replicas using plants that get them when they sleep.
Sleep . . . Sleep . . . and be born again into a world without fear and hate!
Watch out! They get you while you're sleeping!
The seed is planted...terror grows.
Elizabeth Driscoll: I have seen these flowers all over. They are growing like parasites on other plants. All of a sudden. Where are they coming from? Nancy Bellicec: Outer space? Jack Bellicec: What are you talking about? A space flower? Nancy Bellicec: Well why not a space flower? Why do we always expect metal ships? Jack Bellicec: I've NEVER expected metal ships.
Mr. Tong: No, no... she alright. She betta now. Much betta now.
Elizabeth Driscoll: Yep, Boccardo's pills. He eats it like candy... or used to. Take some. Matthew Bennell: What are they? Elizabeth Driscoll: Speed. They'll keep us awake. Matthew Bennell: How many are you suppose to take? Elizabeth Driscoll: It says take one. Matthew Bennell: Take five.
Dr. David Kibner: Elizabeth, could you please tell me, in your opinion, what is going on? Elizabeth Driscoll: People are being duplicated. And once it happens to you, you're part of this... thing. It almost happened to me!
Elizabeth Driscoll: I keep seeing these people, all recognizing each other. Something is passing between them all, some secret. It's a conspiracy, I know it. Matthew Bennell: There can't be a conspiracy! Elizabeth Driscoll: Matthew, I'm telling you something is going on here.
At the beginning of the film, as the alien spores rain down on earth, you see them presumably landing on the Transamerica Pyramid in San Francisco - the headquarters of what was then the parent company of United Artists, which produced the film.
Cameo: ['Don Siegel (I)'] taxi driver. Siegel directed the original film, of which this film is a remake.
Cameo: [Kevin McCarthy] man asking for help. McCarthy was the star of the original film, of which this film is a remake.
Cameo: ['Robert Duvall (I)'] the priest on the swing.
According to the commentary on the DVD, director Philip Kaufman said they paid 'Robert Duvall (I)' by giving him an Eddie Bauer jacket.