Lord of the Flies starts of with a group of British boys whose plane crashes on a deserted island in the Pacific Ocean.  With no adults, the boys are left to fend for and govern themselves. The boys range in age from six to twelve, and Ralph, one of the older boys, becomes “chief” with the assistance of a conch shell.
The first trouble begins when the boys become fearful of a “beast” somewhere on the island. Troubles aside, they decide it would be best to build a fire to signal any passing ships. To do so, they use the glasses of a boy named Piggy. 
Things heat up when another boy, Jack, jealous of Ralph’s power, decides the boys should devote their energies to hunting food instead of maintaining the fire. Jack, among many others, seems to become more and more savage the longer they are on the island. Meanwhile our other key player, a wise and philosophical boy named Simon, works with Piggy to build shelters.  
It all goes swimmingly until these  conflicts become not so strange and the boys who are supposed to be tending the fire skip out on their duties to kill a pig. The scene makes all the boys seem like primitive savages instead of well-behaved British gentlemen. The blood and gore of the hunt is all very exciting until they realize that, while they were out being bloodthirsty boys, the fire went out and a ship passed by without noticing them. Jack has also managed to punch Piggy in the face and break one lens of his glasses. 
Right about this time a dead man attached to a parachute blows in Mary-Poppins-style to the island. The war going on outside the island seems to be responsible for the fact that he is dead. Anyway, the mysterious parachuting creature is mistaken for the beast, and the boys begin a massive hunt to kill it. Only Simon is doubtful that there is such a creature, believing instead that the beast is part of them, that their fears are only about themselves. He goes off into the woods to contemplate the situation while Jack and Ralph ascend the mountain and find the beast  but don’t stick around long enough to see that it is in fact only a dead man.
Back in the group, Jack decides Ralph shouldn’t be chief anymore. He secedes from the union, if you will, and invites whoever wants to come with him and kill things. Ralph and Piggy set about building the fire, but realize by the end of it that most of the older children have gone, presumably to join Jack. During all of this, Simon is hidden in his nifty meditation spot, watching Jack and Co. hunt a pig. This time, they slaughter a fat mother pig, cut off her head, and jam it onto a stick in the ground.
Simon stares at the head, which he calls “the Lord of the Flies” as it tells him that it is the beast and that it is part of him. Simon passes out, gets a bloody nose, and wakes up covered in sweat, blood, and other generally disgusting things. Despite all this, he decides to continue up the mountain to face the beast. Simon discovers that the beast is in fact just a man. Then he vomits and staggers down the mountain.
By now, Ralph and Piggy are attending a big feast/party that Jack is throwing. It’s all a frenzied reenactment of the pig hunt until Simon, still bloody, sweaty, and covered in puke, stumbles down into the center of the crazed boys. He tries to tell them about the beast, but he is unrecognizable and the boys jab at him with their spears until he is dead. Again, the boys are portrayed as savage animals.

Simon’s body is washed out to sea that night, as is the body of the dead parachuting man. Ralph and Piggy later convince themselves they didn’t take part in murdering Simon.
It’s all downhill from here; Jack’s crew attacks Ralph and Piggy and steals Piggy's eyeglasses to make fire on their own. When Ralph and Piggy decide to calmly talk it out with the “savages,” Roger pushes a huge boulder off a cliff which kills Piggy. Ralph ends up running for his life, finds out that there’s a head-on-stick future planned for him, and at last makes it to the shore of the island where he runs into…an officer of the British Navy. The boys are rescued from their mock war, but we’re left with the image of the Navy’s “trim cruiser” from the real war of the adults.