A plane of boys crashes on a deserted island in the ocean
The group has a vote to decide who is leader, and Ralph is elected leader but Jack doesn't agree with the decision and the conflict between the two emerges.
The conflict among the group has become so prominent that the group has split into two sides, Jack's side and Ralph's side (Jack's side is savage and Ralph's is civilized).
Simon emerged from the brush to let the two groups know that the best was only within them, but Jack and his cult brutally beat Simon to death.
Ralph and Piggy go to tend to the fire but the rest of the group attack them and roll a giant boulder down a hill towards them. Ralph is able to dodge it, but Piggy isn't fast enough and get killed by the boulder.
Ralph escapes the rest of the group, and miraculously runs into a navy seal (who came to rescue them) and tells him everything that happened on the island. Finally the boys are brought back to London.