Spores originating on a distant planet float to Earth, dropping onto vegetation in San Francisco, California. The gelatinous spores sprout into small pods with flowers on the end. Elizabeth Driscoll picks one of these pods on her way home from work and is excited to show her boyfriend, Geoffrey, but he is more interested in the playoffs on television. Matthew Bennell, Elizabeth's co-worker at the Health Department, calls to ask her to come into work early to run tests for him. The flowering pod rests in a glass on the nightstand when Elizabeth and Geoffrey go to sleep. Elizabeth awakens the next morning as Geoffrey sweeps up a pile of broken glass and is uncharacteristically cool toward her. At work, Elizabeth apologizes to Matthew for arriving late, and claims Geoffrey was acting strange. Geoffrey cancels their plans that night and leaves for a meeting. Upset, Elizabeth goes to Matthew’s home and insists that, although it sounds insane, Geoffrey is not really Geoffrey anymore. Matthew suggests that Elizabeth talk to his friend Dr. David Kibner, who is a psychiatrist. Instead of going to work the next day, Elizabeth follows Geoffrey as he meets strangers around the city. Elizabeth then goes to Matthew and tells him that she suspects a conspiracy. Matthew drives her to David’s book party so she can talk to him about her troubles. En route, a man runs in front of their car and warns, “They’re coming!” The man runs off and is hit by a car. At the party, Matthew introduces Elizabeth to Jack Bellicec, an offbeat writer. Elizabeth watches David console a hysterical woman who says her husband is not her husband. Elizabeth tries to intervene, but David waves her aside and convinces the woman to reunite with her husband. When David talks to Elizabeth, he reasons that she is jumping to a bizarre conclusion about Geoffrey, and might be looking for an excuse to leave the relationship. David, however, admits he has heard the same story all week and suggests it is a hallucinatory flu. Matthew wonders if it is contagious, which would mean he would have to get the Health Department involved. Jack is upset about his own writing when he visits the Bellicec Mud Baths. His wife, Nancy, deals with her last clients while Jack relaxes in the steam room. When Matthew drops Elizabeth at her home, they find that Geoffrey has left a plant for Elizabeth. They call out for Geoffrey, but he does not answer, although he is hiding in the house. Matthew leaves and Elizabeth puts the plant on her nightstand. At the mud baths, Nancy thinks Jack is lying covered up on a massage table, but, when she pulls back the sheet, she finds a web-covered, half-formed body. They call Matthew for help. Matthew notes that the body is Jack’s height and weight, but has no details or fingerprints. Matthew tells Nancy and Jack to call David for help, then Matthew leaves to rescue Elizabeth. Jack lies down to rest and, when Nancy examines the body again, it opens its eyes. Her screams wake Jack and, as he opens his eyes, the body’s eyes close. Matthew arrives at Elizabeth’s house, but Geoffrey does not answer the door. Matthew breaks a back window and sneaks past Geoffrey. He sees a half-formed version of Elizabeth lying on the porch while the real Elizabeth sleeps on the bed. Matthew carries Elizabeth to his car, escaping just before Geoffrey returns to the bedroom with a trash basket. David arrives at the bathhouse, but cannot find a body. Nancy and Jack also search, but the body is gone. Matthew brings Elizabeth to the bathhouse. He sends Nancy and Elizabeth to his home while he, David and Jack meet the police at Elizabeth’s home. There is no half-formed body, however, on Elizabeth’s porch, and the police do not believe Matthew and Jack’s story of duplicate bodies. Matthew, Jack and David join Elizabeth and Nancy at Matthew’s home. Matthew wants to institute emergency procedures through his office. Although David does not believe the duplicate body theory, he trusts Matthew enough to agree to call the Mayor for help. When David leaves, he gets into a car with Geoffrey and a policeman; David is one of the pod people. Elizabeth finds a pod flower in Matthew’s home and wants to analyze it at work, but her boss insists that he do the testing. Matthew, meanwhile, speaks with various city departments; every call includes a warning to keep quiet because they do not want to create a panic. The group meets again at Matthew’s home that evening, and David gives Elizabeth a sedative so she can sleep. Before he leaves, David tells Matthew that they have done everything possible and that Matthew should sleep, too. Jack and Nancy settle on the sofa, and Matthew falls asleep on a patio chair. Four large pods grow near him, and unformed bodies emerge from each pod and start to duplicate them. Nancy wakes, sees the pods and screams. Matthew awakens in the patio of pods. Their electrical power is suddenly cut off, the street is barricaded and pod people are outside. Matthew smashes the head of his duplicate with a garden hoe before the group races out the back door. They are chased through the city by the pod people who communicate with a strange shriek. When they are cornered, Jack runs off to distract the approaching pod people, and Nancy follows him. Matthew and Elizabeth find a cab and ask to be taken to the airport, but when the cab stops at a suspicious roadblock, they sneak off. They hide in their office and watch the crowd outside spread pods. Jack, who is now is a pod person, helps capture them. David gives Matthew and Elizabeth a sedative to help them sleep so they can evolve into a new life form. He tells them that their minds and memories will be intact, but they will not have any emotions. Matthew and Elizabeth fight back; they kill Jack, lock up David, and escape. Nancy runs into them and explains that pod people can be fooled if you do not show any emotions. They are able to blend in with the crowds until Elizabeth is shocked by a mutant pod person, and her scream ignites their strange shrieks. Matthew and Elizabeth escape in a truck while Nancy blends back into the crowd. The truck arrives at a warehouse where pods are cultivated. Elizabeth twists her ankle, and Matthew carries her to a hiding spot. They hear the song Amazing Grace coming from a nearby ship, and realize there is a chance for escape. Matthew rushes to check on the ship, only to find it is being loaded with pods. He runs back to Elizabeth, but he is too late. She is asleep, and her body collapses into a pile of dust as her pod duplicate arises. Matthew runs inside the plant and climbs into the rafters. He grabs an ax and cuts the wires to overheard lights, igniting a fire. Matthew escapes through a window as explosions ripple through the building. He then hides underneath a pier as pod people search overhead, and tries to stay out of sight when a pod person shines a flashlight through the boards. The next day, Matthew is emotionless as he works at his office. His co-workers, including Elizabeth, also go through the motions, although no work is accomplished. When Matthew leaves and walks through the park, Nancy sees him and calls out quietly. As Nancy approaches, Matthew points at her and shrieks.