The film opens with a montage of transparent amoebalike organisms leaving their planet, somehow, and floating on the cosmic winds towards Earth. Some land and take root in San Francisco, becoming a pod with pink flowers. The next scene introduces our hero, Matthew Bennell, a health inspector for the San Franciso Health Department, giving a surprise visit at a French restaurant. I love this character because he is a government employee, but he isn't the typical cop or military type. Next, a lab tech from the Health Department, Elizabeth, finds one of the plants and brings it home to the house share with her boyfriend Geoffrey. The next morning, the plant is missing, and Geoffrey begins to act strangely. Concerned, Elizabeth turns to Matthew for help. He offers to introduce her to his psychiatrist friend David Kibner, but then the next day Matthew is approached by his dry cleaner, telling Matthew that his wife is acting like an imposter, the same way that Elizabeth was describing Geoffrey.
At a party, Matthew is able to introduce Elizabeth to Kibner, who is trying to calm a distressed woman who is also explaining that her husband isn't who he is. He tells the woman that she has nothing to worry about, the same advice he gives to Elizabeth. Feeling dismissed, Elizabeth leaves for home. Also at the party is Jack, played by Jeff Goldblum (Mr. Frost), another friend of Matthew, who personally has issues with Kibler's work. The film then follows Jack as he returns to the mud bath spa that he operates with his wife Nancy, played by Veronica Cartwright (Alien), and the clients that are passing their time at the spa. Jack becomes lethargic as Nancy finds an unfinished body double of her husband laying on one of the massage tables. They contact Matthew, who brings an unresponsive Elizabeth with him. The four realize that something of a large scope is taking place and that they are all in danger.
Over the course of the following day, Matthew finds evidence of the replacement of the people he knows around town. When he tries to call his government contacts, he finds that they've been compromised as well. Matthew and Elizabeth come to realize that everyone is being replaced by a pod, and when one is near you, it takes your form while you sleep. That night, Matthew, Elizabeth, Jack, and Nancy try to elude mobs and authorities when they find out that they are some of the last humans left in the city. Kibler is leading the search for the humans, explaining that everything is so much easier after the change. One by one the group is split up, and despite his best efforts, Matthew is unable to keep Elizabeth from being replaced. Matthew is able to burn down a warehouse full of the pods, but his efforts may be in vain. Sometime later, a day or two, Nancy comes across Matthew, who she thinks is still pretending to be a pod-person. To her horror, he points and screams!
Matthew and Elizabeth pretending to be "replaced"
