SPOILER: sent in by VoxAngelikus.
At 3:03 p.m. Eastern Standard Time on Oct. 1, something called The Pulse begins to emanate from cellphones everywhere across America, and those using, or even listening to, cellular phones, begin to savagely attack one another. The main character, Clay Riddell, is in Boston Common, having just signed a major graphic novel deal, and has stopped for ice cream before going back to his hotel to call his wife and son back home in Maine to tell them all about it. That's when The Pulse happens, and all hell breaks loose.
People viciously attack each other, fires break out, and the city of Boston burns. Clay meets up with Tom, a gay man, and Alice, a 15-year-old girl who lost her mother to The Pulse. They escape Boston and make it to Tom's house, in a suburb outside of the city. Clay's plan is to make his way north, back to Maine, where his estranged wife and son (who may or may not have been using a cell phone) live.
The next day, the begin to notice that the "phone-crazies" are not so crazy after all. The zombie-like people "flock" in the morning to scavenge through towns, returning in the evening to sleep in some unknown location. Travelling by night, Clay, Tom and Alice acquire guns and rations and begin the journey northward. They have become "flashlight people" and follow other straggling groups of survivors, all heading north.
Along the way they come to a place called the Gaiten Academy, where an elderly headmaster and the sole remaining student, a 12-year-old genius named Jordan, show them the source of an endless stream of soft-rock music. Hundreds of "phone-crazies" are lying on the school soccer field. The headmaster, Charles Ardai, explains to them how the "phone-crazies" are evolving, beginning to develop powe! rs of telepathy, telekinesis, and shared-thinking. Together, the group of five commandeers two propane trucks from the local town and drive them into the middle of the field while the "crazies" sleep. Clay shoots one of the trucks, resulting in a tremendous explosion which wipes out all the "phone crazies".
Before they can leave the Academy, however, they begin to have shared dreams of being placed on platforms in front of a large crowd, while a zombified black man in a Harvard sweatshirt (called The Raggedy Man because of the way his skin is torn and ragged on his face) speak in Latin, calling them each insane, to which the crowd responds "Don't touch". The only one who cannot remember this dream is Alice, for reasons that are discovered later.
The Raggedy Man then shows up at the Academy, and in retribution, all the non-phone crazies in the town are violently killed in retribution. He then lets them leave, instructing them to follow an ominous message which has been popping up everywhere: KASHWAK=NO-FO. Before leaving, The Raggedy Man enters the mind of the Headmaster, and makes him commit suicide by shoving a pen into his own eye.
The group starts to head north again, but now no-one on the road wants anything to do with them. The "phone-people" have all had dreams where the Raggedy Man has told them not to touch Clay, Tom, Alice or Jordan, because of what they've done. Along the way, their dreams continue and eventually they come to include another group of people, who they meet up with later on in the story.
As they near Clay's hometown, they are passed on the road by a "sprinter", a car full of men driving at breakneck speed down the highway. Their car crashes and they have an encounter with the group that results in Clay's pistol-whipping one of the men. Later, the same ! two men encounter the group again, only this time, one of them throws a cinderblock out of their moving car. The stone hits Alice in the side of the head and she takes that night to slowly die.
Now they've reached Clay's hometown, but all that is left of his wife and child are two notes from his son, saying the wife has been turned into a phone-person, and that he is going to Kashwak, a town in Northern Maine where a large state fair is held. Kashwak is also a cell phone dead zone. Clay decides he is going, even though they all agree that it is nothing more than a trap set up by the Raggedy Man. Before splitting up, they meet the other people from their dream, another group of survivors that has destroyed three "flocks" of phone-people. Clay separates from them and goes to find his son. Along the way, he sees in his dreams what is happening at Kashwak; survivors line the sides of the road, in line to enter a tent where "phone people" telepathically force them to pick up cellular phones and make calls, thus transforming them. The Raggedy Man's trap, however, is flawed, as there was a flaw in the original Pulse, a worm that continually corrupts The Pulse so that each time someone uses a cellular phone, the result is different than when everyone's minds were wiped clean the first time the Pulse was emitted.
Clay eventually comes upon his friends again, who let him know that The Raggedy Man has been controlling their minds, making them confuse real waking life with their dreams, and telepathically joining them together again, so they can be executed for the crime of having killed phone-people. They are in possession of a school bus now, and before they can leave, one of the members of the second group of survivors takes Clay aside, hands him a cell phone and a number to call. He tells Clay that God-willing, Clay will know when to call the number. The man then kills himself. After that, The Raggedy Man appears, the group unwillingly throws away all their weapons, and travel with the Raggedy Man on the bus.
The group ends up at the Kashwakamak Fairgrounds, the place they have been dreaming about. They are locked in a large casino hall where they are to wait until the next day, when they will be executed. Clay comes to the realization that the reason the man killed himself after giving Clay the phone and phone number did so because he packed the back of their school bus with explosives. Jordan, the youngest, wriggles through a broken window, goes across the fairground, drives the bus to the middle of the field, where thousands of phone-people lay sleeping (some who have heard the modified Pulse, stagger around).
The carnival/fairground workers had installed an illegal cell-phone transmitter at the top of the parachute jump ride, so that they would be able to communicate with each other while setting up the fair and rides. Now, Clay is able to see that the cell phone he was given has 3 bars. The other cell phone, which the man had set up as a detonator on the school bus, also has 3 bars. Clay dials the number, and the entire fairgrounds goes up in a giant fireball, killing almost all of the phone-people, Raggedy Man included.
Now the group decides to keep going north, where there is no cell phone service, and where they are sure the coming Winter will kill the majority of the remaining phone-people. Clay again separates from them, electing to try and find his son. They agree to a plan where Clay will be able to follow them and meet up with them again. Jordan tells Clay of a possible way to get his son back, should he find him. The idea is that the Pulse will eventually collapse, due to the worm in its system. Jordan feels that if Clay were to make his son listen to a cell phone call again, it could wipe his mind clear, and that all the boy's original thoughts might slowly return, as they could have been stored deep in his brain.
Clay journeys, looking for his son, until he actually finds him. But it is only his son in body, as his actions are like that of a beaten dog. They start to travel north again to find Clay's new friends, and the book ends with Clay nervously dialing a phone number and putting the phone to his son's ear, in the hopes that it might save him.