An alien lands on Earth and starts to spread its slug-like offspring.
What appears to be a rock falls from space. In Wheelsy, South Carolina, Wally and Bill Pardy are sitting in their patrol car. Wally uses a speed gun to measure the speed of whip-poor-will, which surprises him as he thought it would be faster. The object from space then crashes into the woods of Wheelsy. As Jack MacReady is driving through town, he starts honking at Inconsiderate Driver who has left his vehicle parked in the road while he goes shopping. He calls the Inconsiderate Driver a vulgarity and then looks over and sees Upright Mom and her daughter staring at him and Upright Mom tells Jack, good morning. Starla Grant is teaching her class about survival of the fittest when Kylie Strutemyer looks over and sees Drawing Boy drawing a nude picture of Starla. After school ends, Hank is talking with Starla when Grant Grant comes to get Starla and accuses Hank of trying to pick Starla up. Trevor and Margaret are helping children cross the streets when Trevor wonders why Starla married Grant. Margaret tells him it was because Starla grew up poor and wanted to have a better life. Bill makes a comment about Grant not having a vagina and 'Gina Kid asks what a gina is and Bill tells him like the Ginese people.
At night Grant tries to have sex with Starla, but she tells him that she isn't in the mood and he angrily leaves. He goes to the bar where Karaoke Woman is giving a rendition of The Crying Game. Brenda Gutierrez walks up to Grant and Grant remembers her. They leave the bar and go into the woods and start kissing, but Grant stops due to him being married to Starla. They see the space object which is cracked open and find the The Long One. As Grant pokes at it, a barbed appendage suddenly shoots out and embeds itself in Grant's chest and travels to his brain. Grant then walks away and drives home and eats meat. In the morning, Starla apologizes to Grant, who starts crying and they have sex. At work, Janene notices Starla is in a good mood and Starla tells her that Grant seemed different in a good way. Grant goes to the grocery store and buys 14 rib eyes from the Butcher and lots of other meat. Starla notices Grant has added a lock to the basement and he tells her it is because of a birthday surprise for her. Grant's body starts to change and he grows two spiky appendages. As he is about to attack Starla, he stops and tells Starla that he has to go to work. At the Deer Cheer, Lead Singer and his band play. Grant goes to Brenda's house and she lets him inside. Bill walks up to Starla and they awkwardly talk. Jack gets up to make a speech about how after God invented Earth he said man should have dominion over animals.
Brenda takes her shirt off and Grant does too. He then attacks Brenda with his spiky appendages and impregnates her. Starla goes home and finds Grant has physically changed and he tells her that he got stung by a bee and he already saw Dr. Karl. The next day Starla calls Dr. Karl and he tells her that he hasn't seen Grant in over a year. As Starla is driving home she notices a large amount of missing pet posters. Grant brings meat to a chained up Brenda. Bill and Wally go to Starla's house and ask to see Grant. They tell her that Grant was last seen with Brenda who is now missing. Starla breaks into the basement and finds it full of flies and dead animals. She calls Bill's number and leaves a message. Grant sees her calling through the window and goes into the house and attacks her and attempts to infect her. Bill, Wally, Trevor and Margaret walk into the house and Grant runs away. Three days later, Jack complains to Tourneur and Bill about the city council wanting Grant found, as a Sad Drunk waits to be processed. Jack worries that Shelby is going to cause a hysteria when he hears Bill describe Grant as squid looking. Jack gets upset when Wally, Trevor and Margaret aren't taking things seriously and suggests Grant might just have lyme disease. Shelby tells Bill of another animal attack and he, Wally, Trevor and Margaret drive to the location. Bill has a meeting with the other officers, Jack, Charlie and Dwight. He tells them that he thinks Grant will next attack the Strutemyer property. Before they leave, Starla demands to go with them.
Mrs. Strutemyer gets upset with Emily Strutemyer and Jenna Strutemyer for playing at the dinner table. She notices Kylie painted her fingernails and Mr. Strutemyer thinks it looks like a Pokemon did them. They drive to the Strutemyer property and wait for Grant. He eventually appears and kills a cow. Starla walks up to him and talks to him. Charlie points his gun at Grant and demands he show them where Brenda is and Grant uses a tentacle to cut him in half. Bill and the others start shooting at Grant and he slithers away. They follow him and end up at a barn where they find a severely enlarged Brenda. She tells Bill that she is hungry and then her body starts to tear apart and explodes. Thousands of worm-like things pour out of her. They go into the mouths of Wally, Trevor, Tourneur, and Dwight. The worms slither to the Strutemyer house where Kylie is taking a bath and Mrs. Strutemyer tells Emily and Jenna it is late and they need to stop reading their Goosebumps books and go to bed. A worm thing attacks Kylie and goes into her mouth and Kylie has an image of The Long One attacking creatures on another planet. She then sees what has happened since The Long One attacked Grant. Kylie manages to pull the worm thing out of her mouth and kill it and runs out of the bathroom and finds Emily, Jenna, Mrs. Struemyer and Mr. Strutemyer already infected with the worms. She runs outside and gets into the family truck and hides.
Bill tries to contact Shelby, but can't reach her. Starla, Jack and Margaret drag the bodies of Wally, Trevor, Tournier and Dwight out of the barn, and the bodies suddenly get up. Wally and the others start talking to Starla as if they are Grant. Kylie's family also get back up and tell her to join them. Trevor spits a yellow liquid onto Margaret which makes her skin burn and enlarge. Wally zombie threatens Starla and she shoots its head off and a worm comes out. Bill sees Kylie and she runs to him. Fitzgibbon attacks Bill, but Bill and Kylie manage to get into his patrol car. They see Starla and Jack being chased and Bill uses his vehicle to ram Trevor and Starla uses a T-Post to kill the Trevor zombie. Starla and Jack get into the car and Bill is able to get in contact with Shelby and she tells him that his mom called and said the toilet in the house was clogged from what he did the weekend before. Shelby is then attacked by the worms. Kylie tells them about what she saw when the worm attacked her. As they are driving back into town, they are rammed by a vehicle. Starla is dragged away by the zombie horde along with Jack, but Bill and Kylie manage to get away. Bill comes up with the idea of killing Grant to stop the infestation and goes to the police station. He goes inside the police station and is attacked by a zombie deer, but is saved by Kylie. He grabs a grenade and then gives Kylie a gun. They start to walk towards Starla's house and see Gleeked on Guy getting spit on.
Jack regains consciousness and finds himself in the basement surrounded by impregnated people eating raw meat. Woman in Basement gets upset with him for looking at her and tells him he has no idea how hungry she is. He opens the basement door and is impregnated by Grant. Jack is brought back down into the basement and he starts eating a dead body. Starla wakes up on her bed and goes downstairs and sees a giant Grant mass. Bill and Kylie watch as Dude Joining Grant becomes one with the Grant mass. Diseased Grant 1, Diseased Grant 2, Diseased Grant 3, and Diseased Leader accuse Starla of being unfaithful and wanting to kill Grant. Starla apologizes and tells him that he doesn't have to be alone. She walks up to him and stabs him with a hair brush she had hidden. Grant then knocks her away. As Bill and Kylie are almost at the house they are seen by Brenda's Husband. Bill shoots him dead meanwhile, Kylie is grabbed by Head-Shot Norman and she shoots him in the head. Bill and Kylie enter the house and a deformed Jack asks Bill to kill him, which he does. Bill and Kylie reach Grant and Starla and Bill tries to throw the grenade, but it is knocked out of his hand by Grant. He finds it again, but is knocked out of the house and it harmlessly explodes in the pool. Grant throws a couch at Kylie and knocks her to the wall. He extends his pincers and starts to impregnate Bill with one of them, but Bill manages to stick the other one into a propane tank and turns it on. Bill tells Starla to shoot Grant and she does and he explodes. All of the zombies fall to the ground and Starla and Kylie check on Bill and he pulls out the Grant tentacle. Kylie tells him both tentacles had to inject him for him to become impregnated and they walk out of the house and walk away.