In a lab, geologist Dr. Jonas Temple examines two strange rock samples that a student brought in as his lab assistant Laurie Cameron looks on. Laurie puts the two rocks in a cabinet and the two scientists return to work. Laurie's husband Paul, a surgeon, comes in to remind Laurie that it's lunch, and as she goes to get ready Jonas and Paul chat briefly. Once Jonas leaves, the fire in his lab oven goes out and Paul lights it back up.
There's an explosion, knocking Paul back. The two rocks in the cabinet pulse and telepathically "talk", saying that the time is there. Paul hears them in his mind as they wonder if it's safe to communicate with someone present. Paul looks around, puzzled at who is talking, as the rocks discuss which humans to take over. They realize that something is wrong with Paul's head, and figure that he's injured. The rocks discuss how once they control the humans, they can control the planet. Paul staggers to his feet and calls out to whoever is talking, and the rocks realize that they can hear him and figure that they must kill him.
Laurie comes back in and Paul passes out. Later she takes him to the doctor, Ralph, who puts a metal plate in Paul's head and confirms that there's no fracture. Ralph assures Paul that he has nothing to worry about in the way of brain damage, and the couple goes back to the lab. They tell Jonas that Paul is all right, and Jonas apologizes for the faulty oven. Laurie massages Paul's head and discovers that he's shaking. He says that when he was lying on the floor he heard inhuman voices. Paul describes what they said and how they threatened to kill him. He figures that they would have if Laurie hadn't come back. Laurie and Jonas dismiss it as shock, but Paul doesn't believe it. They look around the lab to discover the source of the voices, and Laurie points out that there's only rocks and rocks don't talk. Paul notices that literature is filled with stories of rocks speaking, moving, and weeping.
Jonas concedes the possibility of a rock-like alien lifeform, and points out that they must be parasitical viruses. However, he finds the whole concept unlikely and advises Paul to forget about it. Paul hears the rocks talking to him. They say that "listeners" must be destroyed, and Paul tells Jonas that it's started again. Jonas and Laurie don't hear anything, He checks the various rocks, and the rocks take mental control of Paul, telling him to jump out the window. Laurie and Jonas pull him back just in time, and Laurie takes Paul home.
Once he's alone, Jonas goes to the cabinet and picks up the two alien rocks that Paul picked up during his search. One of them sprouts tentacles and crawls onto his hand. It then forces Paul to clutch his face with his hand while the other rock "looks" on.
At home, Paul sits in the darkness with the doors and windows locked, and the phone rings. Laurie starts to answer it, but Paul tells her to forget it. She wonders why, but Paul just says to leave it alone. He wonders what he's afraid of, and desperately hugs Laurie. Someone knocks at the door, and Paul tells Laurie not to answer it. She opens it anyway and finds a drunken neighbor outside. She closes and locks the door, and Paul goes to it and unlocks it to overcome his fear. Paul turns on the lights and says that it's easier to imagine spooky voices than worry that he's going insane. He asks Laurie if she really believes he heard voices from aliens, and Laurie asks if anyone can prove that he didn't. Paul notes that he has symptoms of paranoia, and Laurie suggests that they go away. She points out that they never had a honeymoon, and she picked Mexico when he gave her a random choice. Laurie tells Paul that she'd go there with him immediately, and Paul says that he wants to run. In a few days his paranoia will pass and then he'll be all right.
Laurie agrees and goes to the bathroom, and the phone rings. Paul tells her not to answer it and leads her out. A now-white-haired Jonas stands at the lab trying to call, and the alien possessing him tells the other rock that Paul doesn't answer. The alien tells Temple to find Paul wherever he is before he speaks to others who might believe him. Temple promises that he'll find out where Paul went and kill him, and the alien suggests that Laurie might lead Temple to Paul. He picks up the alien rock and leaves.
The Camerons drive to Mexico and drive to a rental home in the middle of nowhere. The Caretaker leads them inside and warns that the house hasn't been lived in in a long time. He agreed to watch over it until his friend came back, and the Caretaker goes to get firewood and assures them that they won't be disturbed. Laurie insists that it's okay and they go to bed.
The next morning, Laurie looks around to see what they need to make the place livable. Paul says that he'll drive into town to shop, and call his hospital to say that he went AWOL. Laurie says that she called the hospital from the tourist office, and assures him that it's going to be all right. Paul suggests that he's hearing voices because of the plate in his head. When Laurie starts to get dressed, Paul tells her that he wants to go alone and promises that he won't be gone long.
As Paul leaves, Temple watches from the brush. He then walks to the house and goes inside. Laurie sees him and realizes that he's changed, and the alien asks when Paul will be back. He grabs her arms and demands answers, then takes out the second rock and pushes Laurie's face onto it.
Later, Paul returns with supplies. Laurie is lying on the bed and Paul notices the Caretaker outside, making a circle of fire. He calls to the Caretaker, who says that the fires keep away the possessed. The Caretaker warns that an evil spirit has entered some unfortunate being, and goes back to tending the fires. Paul goes into the bedroom and discovers that Laurie has been possessed as well. She yanks Paul to her, and Paul runs to the car and drives off. The Caretaker looks at him for a moment and then goes back to tending the fire.
Paul gets a hotel room in Tijuana and makes sure the door is locked from the inside. He hears a woman in the hallway saying that she found him, but realizes that it's another woman talking to her boyfriend. Paul dozes off and has a nightmare, and wakes up sweating. He washes up and opens the door to go out, and finds the Caretaker in the hallway. The Caretaker says that Laurie is sick and needs a doctor, and she's suffering from a fever that affects many people. He tells Paul that Laurie is dying, and Paul drives back to the house. Paul examines the unconscious Laurie, and goes to the kitchen to prepare an injection for her.
Once the Caretaker leaves, Temple comes in and draws a gun on Paul. He says that he must kill the listener because he's a danger to them, and shoots Paul in the shoulder as Paul backs away. When Temple moves in to take a second shot, Paul knocks a gun out of his hand and the two men struggle. They fight and Temple knocks Paul to the floor. As he says that Paul is making them lose time, Paul grabs a scalpel from his kit and stabs Temple as the possessed man tries to strangle him. Temple finally dies and the alien rock appears on his face.
The possessed Laurie picks up the gun and comes out of the bedroom, while Jonas' rock crawls toward Paul. He jumps her and grabs the gun, and tries to get through to the real Laurie. She chokes him and Paul is forced to shoot her as well. Her rock leaves her and the two aliens try to telepathically force Paul to drop the gun. Paul drops the gun but burns his hand on the stove, breaking the spell. He knocks the stove over on the two aliens, picks up Laurie's body, and goes out. The Caretaker watches and tends his fires as Paul drives away.
Written by Gadfly on Jan 11, 2018