After a group of boys find themselves stranded on a deserted island, ranks begin to form. Ralph is elected leader of the boys, and he appoints Jack as leader of the hunters.
Ralph establishes rules to maintain order during meetings. Fear starts to spread among some of the boys who realize they might be stuck on the island for an indefinite amount of time. They are further shaken after one of the boys mentions seeing a beast on the island. The boys attempt to light a signal fire, but mistakenly set nearby trees on fire, angering Piggy who mentions that one of the boys is missing.
Tensions between Ralph and Jack grow after Ralph criticizes Jack and some of the other boys for not contributing to their efforts to build huts for the younger boys and for failing to catch a pig. Meanwhile, Simon finds an idyllic location on the island.
Ralph and Piggy spot a ship in the distance, but the signal fire has gone out. Ralph is furious with Jack and his hunters who were supposed to maintain the signal fire, however, Jack, overjoyed and in a frenzy after finally catching a pig, ignores Ralph’s complaints. After Jack assaults and breaks Piggy’s glasses, the boys roast the pig and dance manically around the fire.
Ralph blows the conch shell and calls a meeting to reiterate the importance of keeping the signal fire lit and to reassure the littluns that there is no monster on the island. The meeting quickly turns to chaos, and after Jack and the other hunters run off, only Ralph, Piggy, and Simon remain. Piggy and Simon assert that they need Ralph’s leadership and guidance.
The twins, Sam and Eric, mistake the body of a dead parachutist for the beast, and after informing Ralph, the boys organize an expedition to search the island for monsters. The boys encounter an unexplored part of the mountain, and Ralph and Jack share a friendly moment. Ralph upsets the boys after scolding them for having fun rather than searching for the beast.
The boys reenact the boar hunt from earlier in the day with a boy named Robert pretending to be the boar, but the boys take things too far and almost kill him. Though Ralph does not think they should hunt for the beast later that night, he joins the hunt. The boys become horrified after witnessing a giant ape-like figure.
Jack separates from Ralph’s group and forms a tribe of his own. Jack and his group leave a pig’s head on a stake in the clearing as an offering to the beast. Simon returns to the beautiful site he discovered, but finding the pig on the stake covered in flies, he begins to hallucinate that the head is talking, claiming itself to be the “Lord of the Flies” and warning him that there is no escape.
Simon discovers the dead body of the parachutist and realizes that the boys mistook it for the beast. While at Jack’s feast, a storm hits the island, and the boys begin dancing frantically in the rain. When Simon emerges from the woods hoping to tell them about the reality of the beast, he is attacked and murdered by the boys who mistake him for the beast.
Ralph is ashamed of the events of the previous evening, while Piggy refuses to accept his role in the murder of Simon. Jack rules his tribe on the Castle Rock, the top of the mountain, and decides to raid Ralph’s now-small group. Jack and his tribe attack Ralph and Piggy while they sleep, and they steal Piggy’s glasses in order to make fire.
Ralph and Piggy decide to go to the Castle Rock to convince Jack to return Piggy’s glasses and listen to reason. Ralph and Jack begin to fight, ultimately leading to Piggy’s death, as well as the destruction of the conch shell. Ralph escapes to the jungle, while Sam and Eric are tortured and pressured into joining Jack’s tribe.
While hiding from Jack and his group, Ralph discovers the skull of the pig, removes it from the stake, and decides to use the stake as a weapon against Jack. Jack proceeds to set the jungle on fire in order to find and kill Ralph. Ralph runs for his life until he arrives at the beach where he finds a naval officer who says they have come to rescue them. As Jack and the other boys arrive, they are gripped with shame as they realize what they have done.