Clay Riddell arrives at the Boston airport and calls his wife Sharon on his cell phone, telling her he made a deal that will result in his being paid for his graphic novel and its adaptations. She is happy but when Clay says he has to fly to Manchester, she tells him he left a year ago. Still, despite his lack of interest in getting back together, he wants to talk to his son Johnny. While Clay and Johnny are talking, Clay's phone stops working and he goes in search of a charger. When he can't find one that is not in use, Clay calls Sharon back on a pay phone.Then everyone who is using a cell phone reacts as if hearing a very loud or annoying noise. Some people are incapacitated, and some commit violent acts. Calling 911 on a cell phone just turn a person into one of them. The police are overwhelmed. An airplane crashes. Clay escapes the airport by the subway entrance, and he finds conductor Tom and several others on the train, but the power is out and the train won't move. Tom suggests walking down the tracks. Soon, the group encounters what are later called "phoners" who behave like zombies. Most members of the group are attacked but Tom and Clay escape through a manhole. Boston looks like a war zone, with abandoned wrecked cars and fires burning. Tom and Clay manage to make it to Clay's apartment while a motorcycle rider is attacked by more phoners. Clay's creepy art is on the wall. The movie's villain, it is later revealed, looks like one of his characters.Clay is desperate to call Sharon but Tom thinks it's not a good idea, since it might still not be safe to use a cell phone. Clay tries texting but the response is gibberish. There is a knock on the door. Alice, a neighbor, is covered with blood and says her mother was killed. She pleads to stay in the apartment. Clay offers to let Alice put on some of his clothes, and they stay in the apartment for a while, closing the blinds so they will not be seen.When the group ventures outside, they find a house near a cell tower and numerous electric transmission lines, with a vehicle with numerous bumper stickers indicating whoever lives there feels very strongly about the right to own guns for defense. Inside several people are dead, some holding guns. Tom, Clay and Alice take all the guns and ammo they can find and go outside. There they see a young man looking dazed, with a small dog. The young man turns around and has a look on his face indicating he is one of the phoners, and he is shot. Other phoners appear and the group shoots at them. Then the phoners appear to respond to a signal, and all of them turn away. A noise is coming from their mouths, which changes. They start walking away. It is determined the phoners sleep at night.After dark, the group arrives at Gaitan Academy, where only Headmaster Charles Adai and student Jordan are left. The group is offered hospitality, and they are shown thousands of phoners sleeping on the school's soccer field. Charles thinks night is when they "reboot". While the group is inside the school, Charles offers the theory that the phoners have been turned into a single organism like a beehive with all members acting on behalf of the group. He also theorizes this is the next stage in the evolution of humanity, a world without disagreement or war. The others do not think this is a good thing, and they want to stop the phoners from hurting the "normal" people that are left. Charles suggests using the truck that sprays the athletic field, but spraying gasoline and setting it on fire. When the field is set on fire, some phoners appear to try to escape. But the fire spreads to the truck and it explodes. Charles is killed and the group leaves.It starts snowing and the group finds a drive-in theater where they can take shelter. The audio is Tom either quoting scripture or preaching a sermon about the consequences of sin. Eventually, Tom is shown speaking. The group goes to sleep but Clay has a nightmare about a deformed man in a red hoodie, similar to Clay's creation. The others had a similar dream. Because Clay's graphic novel has events similar to what is happening, it is suggested Clay either caused what is happening or knows how it will end, but Clay his no such ability. Outside, there is a pile of burned cell phones and Clay adds his to the pile.The snow comes down harder as they move on. Then after the snow stops, in an area where no snow has fallen, they see a restaurant with a sign on top saying "Kashwak No Fo". Kashwak is place in Maine where there is no cell service ("No Fo" means "no phone"), so the group concludes that is where they will be safe. They go inside the restaurant and the people there are grateful to see other "normal" people. The group gets to relax and even have fun. Alice plays a guitar, and Tom looks for a telephone-related song on the jukebox. He settles for "Ring My Bell" by Anita Ward. Alice lip-syncs wearing sunglasses and the others dance. Then Clay and Alice have a serious conversation. Tom has also talked about his life, telling how he came home from Vietnam and wasn't treated right but had a friend who helped him cope, and wondered if the friend was still alive (apparently meaning before everything started happening). He also said he thought it was the end of the world when he lost money in the 2008 recession and then his marriage ended. Clay says he had a career creating graphic art for business and hated it, so he left his family and started writing graphic novels.As the group sleeps, Sally, one of the people already in the restaurant, wakes up and appears to receive a signal, turning her into a phoner. The others who were already in the restaurant also change. Tom, Clay and Alice fight them and Alice is fatally injured before Tom, Clay and Jordan leave. Outside, Alice has some poetic last words, and the remaining group members move on.The group's next encounter with people is in the woods where Ray and Denise are camping next to a Mister Sundae ice cream truck. The group members convince Ray they are not a threat, and everyone gets to eat. Ray behaves like a survivalist and warns the others that he has kept himself from changing my staying awake, because he believes the phoners can take over a sleeping person. He also says there is a casino now at Kashwak, so it will not be a safe place to go. If anything, it is the place The President of the Internet (the man in red that has been in nightmares, also known as Raggedy Man) is calling everyone to. Denise's son who has changed has a hood over his head so the phoners won't find him, and she tries to feed him. Then Clay hears his son's voice coming from Denise's son. The hood is removed and the son says, "Hi, Dad" and Clay has to kill him to protect himself.Ray's behavior becomes increasingly bizarre, and he finally hands Clay his old cell phone and gives him a number to call when the time comes, before blowing himself up. Inside the ice cream truck, there are numerous explosives. Clay and the group take the truck to his family's house where he finds a message from Johnny saying his mom is one of "them" and that he went to Kashwak. Hearing a sound in the attic, Clay goes up and finds Sharon, now a phoner, and he has to kill her to keep from being killed himself.Clay says the others should go on without him and find a safe place to go. He gives Jordan a spray paint can telling him to spray "TJD" for Tom. Jordan and Denise so he will know where to go. Clay hugs Tom and says he could never have found a better friend when the world ended.Clay takes the truck to Kashwak and discovers a large tower, and thousands of phoners walking in a circle around it. The man in red is at the center. Clay tries to kill him and is unsuccessful, then he finds his son in the group looking dazed. Clay calls the number on the cell phone and the truck blows up, destroying the tower, killing Raggedy Man and freeing the phoners. Clay and his son, who is normal again, follow the markers left by Jordan to safety.