Yes, a plane crash. Like many many great movies and TV shows- Castaway,Lost, Final Destination, Conair!
In a nutshell, a plane crash strands a bunch of schoolboys on a deserted island, which may or may not contain a monster. The boys struggle with one another and the baser impulses of human nature. If you recognize this as vaguely similar to the plot of TV's LOST, that's because it's exactly the plot of TV's LOST. At least until LOST started to be about things that are ridiculous. :-P
The first chapter begins with our as-yet unnamed protagonist struggling through a rocky forest (SUPER-SPOILER: his name is Ralph). Within a page we are also introduced to a poor kid whose name is not Piggy, but who winds up being called Piggy because that is the absolute last thing he wants to be called. Thus begins a long tradition of people paying attention to Piggy almost exclusively to mock him, so get used to it now.
Ralph and Piggy explore their surroundings a bit, and Golding uses this time to point out that repeatedly OMG GUYS, RALPH IS NOT ONLY JUST THE BEST, BUT SO PRETTY, while Piggy is fat, four-eyed, and asthmatic. Also, within the first three pages, he endures an embarrassing incident involving pooping. So Piggy is not really off to a great start.
From their conversation, in which Ralph is kind of a jerk (more out of childishness than intentionally), it sounds like an atom bomb type of thing was dropped on England, and the kids were being flown to safety when their plane was shot down. Even through all that, Ralph is pretty happy to be free of grownups, and just goofs around while Piggy does all the actual thinking.
And that friends, is all I'm giving ya! Enjoy the reading!