In the forest outside of Chester's Mill, Maine, Dale "Barbie" Barbera digs a grave. Once he's done, he takes out a man's corpse from the trunk of his car and dumps it into the grave.
As morning dawns, Deputy Linda Esquivel goes to find Sheriff Duke Perkins, who is relaxing in one of the cells at town hall. She tells him that a local drunk called a backfire but she didn't want to panic anyway, so she came to Duke. Duke assures her that she made the right call and they leave together.
Councilman Big Jim Rennie is having breakfast at Rose's diner. He chats with the owner, Rose, and explains that he'll be working at his car lot so that he won't be able to go to the big game and participate in the parade with the rest of the councilman. As he leaves, Big Jim leaves a $100 tip. When Rose objects, assuring him that he already has her vote, Big Jim smiles and says that they're all in it together.
Big Jim's son Junior and his girlfriend Angie McAlister are in Junior's bedroom, making love. Once they're done, Angie dresses and Junior tells her that he loves her. Angie winces and says that it's been a fun summer, but he has a life to go back to. Junior tells her that he's dropping out of college and Angie warns him that he's throwing away his life. Angry, he says that she's the only one who really knows him and that he's always loved her. When Angie tries to leave, Junior grabs her arm and tries to yank her back. Angie yanks free, shocked and angry, and leaves for her job at the diner.
Julia Shumway, the new editor of the Chester's Mill Independent, gets a call from local woman Andrea Grinnell. Andrea says that she's noticed four propane trucks passing by in the last week, and six in the week before that. She figures that it might be terrorism, but when she reported it to Duke, he told her the town was just restocking the reserves. However, Andrea tells Julia that Duke seemed nervous when he got back to her, and he's never nervous. Julia isn't impressed but agrees to do some digging.
Barbie finishes burying the corpse and drives off in his car.
As Duke and Linda head out to check the report, the town's fire trucks pass on their way to the parade. Linda waves to her boyfriend, fireman Rusty Denton.
As Barbie drives out of town, he calls his employer to report that when he tried to make the deal, "Smith" tried to renegotiate, violently, and Barbie took care of him. Duke and Linda approach and Barbie checks his gun, while Duke notices that Barbie's car has no front tags. As they go by, Linda calls in the rear plates while Barbie keeps driving, keeping an eye on the rearview mirror. Just as the police car passes out of side, Barbie is forced to swerve when several cows cross the road. He goes off the road and gets a flat tire, and discovers that his spare is missing.
The ground suddenly starts shaking violently. The church bells go off and everyone in town feels the tremors. Duke clutches at his chest in sudden pain and quickly pulls over.
As Barbie looks around, suddenly a vast invisible wall slams down in the middle of a nearby cow pasture. He stares in surprise and shock as the wall bisects a cow in half, leaving each half to slide down on opposite sides of the wall. Barbie touches the bloody cow and gets an electrical shock, and then looks left and right. The wall extends as far as he see, judging by the path of destruction that it's left as it passed through nearby buildings just like it passed through the cow. Barbie touches the invisible wall and there's a faint electrical discharge, and his bloodstained handprint remains on it. A local teenager, Joe McAlister, runs over and asks Barbie what happened. Barbie doesn't have an answer for him and when Joe touches the wall, he also gets a brief shock.
Duke tells Linda that his pacemaker skipped a beat, but insists that he's fine now. The other deputies call in and report that the town has lost power and outside phone service. Duke and Linda spot a small prop plane passing overhead.
As Barbie and Joe examine the wall, birds start dropping down from the sky, their necks broken because they flew into the wall. The prop plane flies overhead and slams into the wall... and explodes. Barbie gets the shocked teenager out of the way just in time as wreckage slams down around them.
At Big Jim's car lot, Big Jim heads the explosion and drives off to see what's happening.
Barbie and Joe check the wreckage and find the purse of the pilot, a local woman named Mrs. Sanders. Neither of their cell phones work when they try to call, and Barbie spots a fire truck coming from out of town. The sound of the siren doesn't pass through the wall. Realizing the same thing will happen as it did to the plane, Barbie runs over and tries to flag it to down, and it stops just in time. The fire chief runs out and slams into the invisible wall, and Barbie uses a piece of paper to give the chief a message to call the government.
At local radio station WYBS, DJ Phil Bushey is back on the air after his technician, Dodee Weaver, gets the backup generator working. She warns Phil that nobody else is on the air and Phil figures that they can get big ratings.
Duke and Linda arrive at the wall and Joe tells them what happened. Rusty is among the firemen on the other side and tries to call to Linda, but neither one can hear the other. Big Jim arrives while Duke receives word that there have been more car accidents as people slam into the wall. They go over a map of the area to work out the path of the wall and Big Jim tells Duke that he has a contingency plan. Julia pulls up and Big Jim orders her away, saying that it's a crime scene. Duke tells him that they have bigger things to worry about and has Linda requisition the editor's car. As Linda drives off, Julia wonders who Barbie is but he says that he's not her story. Intrigued, she asks him to show her what is the story.
LA attorney Carolyn Hill is passing through Chester's Mill with her wife Alice Calvert and their teenage daughter Norrie. Carolyn worries that Alice hasn't taken her insulin recently and Alice assures her that she'll be fine. Norris is less than thrilled that they're taking her to a camp for juvenile delinquents for the supper, and Carolyn insists that it's a special program, not a prison. As they consider whether to stop for lunch, two police cars drop by and Carolyn decides to move on.
Barbie takes Julia into the forest and points out the wall. As they follow it, they discuss whether it could disappear as suddenly as it arrived, but Barbie is skeptical. He tells the editor that the Army will soon move in and she figures him for ex-military, but he says he hasn't been recently. They come to a house, split down the middle, and find a woman on the lawn bleeding out from a severed hand. She passes out and Barbie and Julia take her back to the car to get her to the local hospital.
As Dodee tries to get an outside signal through the wall, Big Jim bursts in. When they object, he orders them to let him make an emergency broadcast immediately before anyone else dies.
Junior is in his bedroom fiddling with his butterfly knife and listening to the radio. HIs father comes on the air as Junior starts to cut himself on the arm, and announces that everyone has to stop driving.
Carolyn and her family are driving out of town, arguing with Norrie about her recent behavior. Alice turns on the radio and they hear Big Jim's broadcast. As they wonder if it's a prank, Carolyn sees a truck up ahead... and they watch as it slams into the wall at full speed. Carolyn brakes just in time and as they examine the wall, Norrie suddenly has a seizure. Collapsing to the ground, the teenager mumbles about pink stars as her mothers wonder what to do.
Joe returns home and finds his sister Angie there, looking for their parents. They figure that their father is still out on the road and find a note from their mother saying she went to lunch at a Denny's in Westlake--outside the wall. They realize that they're on their own.
Barbie and Julia take the woman to the medical center, and Julia looks for her husband, Dr. Peter Stumway. There's no sign of him and the orderly says that Peter hasn't worked on Sundays in several weeks.
Down the road, Linda examines the wall and sees the reporters gathering outside. They're unable to communicate through the barrier, and move back when the Army arrives wearing hazmat suits and carrying rifles.
Barbie goes behind the medical center for a cigarette and Angie joins him. She's working as a candy striper part-time and chats with Barbie, unaware that Junior is watching her from nearby. As she talks about how they're trapped like fish in a bowl, she notices a cut on Barbie's forehead and strokes it. Junior, watching, seethes with anger and starts to get out of his truck. However, Carolyn and Alice pull up and Angie helps them get their daughter into the medical center. Barbie walks off and Junior watches him go.
That night, Duke checks on the town hall and finds Big Jim there. The councilman tells Duke that all of the other council members were at big game in Westlake, outside of the wall, Big Jim offers to authorize more police officers on his authority as councilman but Duke warns him that they don't need amateurs with guns running around. Letting the matter drop, Big Jim asks what they should say if people start asking about the propane they've been stockpiling. Duke claims that he doesn't know anything about it but Big Jim points out that he's not as stupid as he sometimes pretends. The sheriff angrily insists that he did what he had to so the town wouldn't go broke. Big Jim advises him to calm down before he stresses out his pacemaker. When Duke wonders if it's a threat, Big Jim smiles and says that they're all in it together.
At the radio station, Dodee manages to bounce a series of signals off the wall. Among them are what seem like alien voices, as well as a broadcast from the Army Corp of Engineers discussing how the "wall" is actually a dome, 20,000 feet high.
Barbie goes back to the farm to get his gun from his car. Junior approaches him as if they're old friends and says that Barbie seems familiar. Barbie ignores him and Junior gets increasingly angry. However, when Julia pulls up, Junior backs off and leaves. Barbie asks Julia about her husband and she explains that she's been checking the roadblocks. She hasn't found him and offers to put Barbie up at her house for the night when she realizes he has nowhere to stay.
The teenagers in town are partying at the bridge when Joe arrives. HIs friend Ben Drake follows him down toward the river and Joe explains that he's looking for some kind of generators that is keeping the dome active. As they talk, Joe has a seizure and collapses, muttering "the pink stars are falling in lines."
Angie returns home and Junior ambushes her. He finally knocks her out when she fights back and apologizes, insisting that he didn't want it to go like that.
Most of the adults in town gather at the bar and Duke arrives to brief them. He explains that so far there are twelve dead and some still missing. Carolyn insists that they're under attack and Alice begs them to get help for Norrie. Duke assures them that the government is working on a solution and asks everyone to contact him if they need anything.
Angie wakes up in an underground chamber, and Junior comes in and tells her that there's no use screaming. He explains that his father built a fallout shelter years ago and that she's safe. Angie has no idea what he's talking about and Junior tells her that it's all connected. Horrified, Angie realizes that her boyfriend is insane but Junior insists that he's the only one who knows what's really going on. When she tries to get out, Junior knocks her back and goes out, locking the door behind him. He goes upstairs and locks the outside door, just as Big Jim sees him across the yard. Junior claims that he was checking on the shelter to see if it's usable, but says that it's flooded. The boy offers his help to Big Jim, who awkwardly hugs him.
Julie takes Barbie to her house and turns on the lights, explaining that they have a backup generator. She show Barbie a photo of her husband Peter and Barbie realizes that it's the man he buried in the woods. Julia insists that her husband will come back and that he's not having an affair, and Barbie says that he's looking forward to meeting him.
As Duke and Linda check the dome wall, Linda talks about how she chose to work overtime rather than spend the day at the parade with Rusty. When she wonders why the dome imprisoned them rather than some other town, Duke says that maybe they're being punished. He starts to tell her about some of the things in Chester's Mill that he's kept from her, and casually touches the dome for the first time. The sheriff clutches at his chest and then collapses as his pacemaker explodes in his chest. Linda runs to him and yells for help.
Outside the dome, the Army surrounds the dome by land and air. Reporters are on the air, telling the people of the world that the dome is an unparalleled event in human history.