Set on a deserted island in the Pacific during an imagined destructive war, Lord of the Flies focuses on a group of British schoolboys. Their plane has been shot down and the pilot killed, leaving the boys without adult supervision. The first two boys introduced are Ralph, the protagonist, and Piggy, a wise, chubby boy.
Ralph discovers a conch shell, and Piggy suggests blowing it to call out to other survivors. After Ralph does so, the boys gather and meet. Ralph is elected as leader of the group. Jack, who led the choir, is put in charge of the hunters. At the end of the meeting Ralph, Jack, and Simon explore the setting, leaving Piggy in charge of the others. Ralph expresses the hope that they are not on an island, thinking that might make rescue more difficult. The search proves they are indeed on an island, and it is deserted. As the explorers return, Jack and the others see a pig. Jack draws a knife to kill the pig but hesitates at the last minute.
Upon returning, Ralph confirms the island is deserted. He tells the others they should keep a signal fire burning on the top of the mountain in the hope that a ship will see it and rescue them. The boys use Piggy's glasses to start the fire. Once the fire is started the boys get excited and the fire rages out of control, killing one of the younger boys, known collectively as the littluns. Piggy thinks the boys should have built shelters first, but he is ignored.
As time passes, only Ralph and Simon work on building huts. Many of the children, and all the littluns, spend their days swimming and searching for fruit. Jack becomes preoccupied with hunting and spends all his time in pursuit of pigs. The boys disagree on which activity is more important.
Piggy and Ralph see a ship passing by the island and realize the signal fire has gone out. They rush to the mountaintop to try to restart it, but they arrive too late. Jack and his hunters return with their first kill. They are ready to celebrate and reenact the hunt. Ralph, however, is furious, and Piggy rebukes Jack. Jack smacks Piggy, and one of the lenses of his glasses breaks.
During the subsequent feast, Ralph blows the conch shell and calls a meeting.The boys meet at the bottom of the mountain. At the meeting, Ralph reiterates that the boys need to work together toward the common goal of rescue. Some of the littluns say there is a beast that stalks the island at night. The older boys try to calm them, but instead their fear spreads to the others. Jack claims to not believe in the beast but says even if it did exist, he and his hunters could protect them. Eventually, Jack says he has no use for the rules and leaves the meeting, the other hunters following him.
That night while the boys are asleep, military planes fight a battle in the air over the island. A pilot parachutes out of his plane and lands dead on the island. The next morning Samneric, who had been tending to the signal fire, see the dead pilot and his parachute, though they don't see clearly enough to identify either. Instead they mistake what they see as the beast. They run away screaming, and another meeting is called.
Piggy wants to avoid that part of the island, but Jack says he and his hunters will get the beast. Jack and Ralph lead an expedition to search out the beast. The boys come across a pig and begin their bloodlust chant. Ralph gets caught up in it as well. Later they see the parachute and come to the same false conclusion as the twins did.
At the next meeting, the boys report there is a beast, though Piggy remains skeptical. Jack tries to seize power from Ralph, but he is voted down. Jack runs away angrily and asks the hunters to join him. Piggy suggests that they build the signal fire down on the beach and avoid the mountain. Ralph concurs. When the work begins, the other boys disappear and join Jack.
Jack and his tribe paint their faces and spend their time hunting. They kill a pig and mount its head on a long stick as a tribute to the beast. Simon, while wandering around the island, comes across the pig's head. Simon declares it to be the Lord of the Flies. He has a vision, and it talks to him, saying the beast cannot be gotten rid of because it is within. Simon faints. When he awakens, he goes to find the others and discovers the truth about the parachute.
Simon comes to all of the boys, including Ralph and Piggy, in the middle of a feast and frenzy. They do not recognize Simon and mistake him for the beast. They pounce on Simon and kill him.
The next morning, Piggy and Ralph feel guilt and try to deny their parts in what occurred. The two of them, along with Samneric, are the only boys (other than the littluns) left who have not joined Jack's group. That night Jack and the hunters sneak into Ralph's camp, stealing Piggy's glasses so they can make a fire. Piggy decides he must have his glasses back and says he will reason with Jack's crew.
The four boys go to Jack's group. When they arrive, Ralph blows the conch. Jack does not want to hear what Ralph has to say. Piggy takes the conch and tries to appeal to Jack and the hunters. While Piggy is talking, Roger dislodges a large rock that rolls down a slope, killing Piggy and smashing the conch. Samneric are taken prisoner, and Ralph flees for his life.
The next day Ralph sneaks up to talk to Samneric, who give him meat and let him know that Jack is after him. Ralph tells Samneric he will hide close by and hope the hunters pass over him, but Samneric betray his presence to Jack. Jack and his hunters set the forest on fire to smoke out Ralph from his hiding place. Ralph runs away and ends up on the beach. When he arrives, he falls down exhausted. He looks up and sees a British naval officer. When asked to explain what happened on the island, Ralph begins to weep. The other boys have the same reaction.