Homer has adopted a pig, but obviously doesn't know how to care for it and just dumps its waste into the local lake.  As Springfield is soon horrendously polluted, the angry locals chase them away to Alaska.
  A character who looks like George Bush Snr, offers President Arnold Shwarzenegger 5 options to tackle the problem, but convinces him to go with option 4 - to destroy Spingfield. They cover the city in a glass dome, and the trapped population wait for their annihilation. Will the Simpsons make it back in time to save the day? Will Homer remember the way?

The government opens a plug on top of the dome and drop in a bomb on a 15minute timer.
  Homer makes it back in time, but foils the town's plan to escape, knocking them back down as escape rope, and even manages to speed up the timer.
  With Bart's help and a motorbike, they ride up the dome walls and Bart manages to throw it out the dome before it explodes - the shockwaves destroy the glass all around them, and they ride down the side, then bounce off a glass plate, then off the Springfield sign, then cross the Springfield gorge (like in the early episode when Homer tried it on Bart's skateboard, back when it was funny), and are saved by a wedgie.
  They are cornered by the George Bush senior lookalike with a shotgun - but Maggie drops a rock on his head to save the day.
  Homer and Bart ride into town as heroes, and Homer whisks Marge off for a romantic getaway.
  Millhouse tries to convince Lisa that her love has died, but he shows up.
  The only casualty is Dr Nick Riviera, who is later impaled by a block of falling glass.
  The people come together to help rebuild the Simpson's home, and Homer ends it all off whacking a nail into his leg, then tearing the tiles back off the roof.
  There's the odd scene during the closing credits, but nothing worth hanging around for.