Roger, Ralph and Jack head up the mountain to look for the beastie, they run into a pig. They get to the top but they realize the "beastie" that the twins saw was a dead parachutist.
Jack and Ralph have a fight and they form two groups. A few boys join Jacks "tribe." Jack kills a pig and has a feast to make kids join his side. Simon becomes delusional and talks to the pigs head.
When Simon comes to the party he crawls from the woods and he looks really dirty. The boys' adrenaline from the party makes them think he's the beast and kill him. That night there's a storm and it washes Simon and the parachutist's body off the island.
Jack's tribe goes to Ralph's camp in the middle of the night and steals Piggy's glasses. When the boys wake up Jack's tribe beats them. Jack would have shared the fire with them but something inside Ralph makes him turn against the other tribe.
Piggy brings the conch up the mountain to try and remind the boys of what they had before everyone split but Ralph and Jack get in a fight and Jack pushes a rock down the mountain. It misses Ralph but it crushes Piggy.
The boys start a fire so they can kill Ralph. When Ralph starts running he's being chased by the other tribe. He gets out of the forest and runs into a naval officer. They're finally rescued!