A plane crashes by a remote island in the Pacific. Two English schoolboys (both in uniform) meet and introduce themselves as Ralph and Piggy, the latter a hated nickname. Piggy is overweight, short-sighted and prone to asthma.
They explore the coastline and find a large shell, or conch, which when blown emits a distinctive echoing sound. More boys emerge from various parts of the island, including a choir clad in gowns. A meeting is convened, and the boys introduce themselves: Jack, Simon, Percival Williams Madison, the twins Sam'n'Eric and so on. Jack believes that as head boy and chief chorister he should automatically be leader, but Ralph is elected by popular vote. Jack remains in charge of the choir, who officially become hunters.
Ralph, Jack and Simon walk around the coastline to see if they really are on an island, and find fruit-bearing trees, wild pigs and a rocky outcrop that lets them survey the territory. Back with the others, they agree a set of rules, starting with a requirement that anyone addressing the group must be holding the conch. Jack is especially keen on the idea of imposing rules.
A small boy asks about the 'snake thing' that he saw when he was hiding in the jungle. Ralph denies that there's any such thing, and Jack vows to hunt and kill it. Jack and the hunters create a fire with the help of Piggy's glasses. A shelter is constructed and a pig is slaughtered - but in so doing, the hunters allow the fire to go out when a plane flies overhead. An acrimonious argument between Jack and Ralph ends with Piggy getting his glasses broken.
Ralph calls a meeting to discuss his concern about the way things are going. He stresses that everything they do should aim towards their ultimate rescue. There is widespread belief that there is a ghost on the island, or possibly a beast that comes out of the sea. A vote is called, and a majority (including all the hunters, but not Piggy) agree that there is a ghost. Jack and the hunters run off to find it. Piggy, Ralph and Simon ruefully bemoan the absence of grown-ups, logic and reason.
A concerted hunt for the beast uncovers a badly injured pilot, the 'snake' being the hose of his oxygen mask. The boys run off in fear, having only briefly glimpsed him. Ralph doubts that a creature that size can be fought. Jack derides this and forms a breakaway group with his hunters. Piggy is glad about Jack's departure.
The hunters strip off their clothes and improvise war paint. They find and slaughter a pig, and impale the head on a spike as a gift for the beast. Later, Simon stumbles across the pig's head, crawling with flies.
A thunderstorm breaks out, threatening the fire. The hunters charge through the camp, grabbing flaming sticks and ignoring the protests of the other children. The hunters have evolved primitive chants and beat rocks with sticks. Jack calls for more volunteers to join his tribe and, when Ralph challenges him as to why he isn't holding the conch, says that it doesn't apply on this end of the island.
Simon finds the pilot, now dead, and is the first to realise what the beast really is. He returns to the camp, but is mistaken for the beast and is beaten to death by the hunters. His dead body floats out to sea.
The next day, Ralph and Piggy try to make sense of what's happening, rationalising Simon's death as a terrible accident. The hunters vow to defend themselves against the beast, no matter what disguise he adopts, and steal Piggy's glasses so they can start their own fire. Ralph calls an assembly, which rapidly degenerates into violence. Piggy calls for order and calm, but the hunters topple a rock on him, killing him instantly.
With Piggy gone, Ralph becomes a fugitive, and is chased through the jungle, unable to block out the shrieks of the hunters. He runs onto the beach, where he encounters the crew of HMS Troubridge, who have come to rescue them. A tear trickles down his face. Flames engulf the island.
