Dark Knight Plot...Spoiler...

So...
As everyone knows, the Joker is our villain...

So Joker makes a public decree that unless Batman reveals himself to the world, He'll start killing the people on his list (Gordon, Dawes, A-List of Gotham City). After this plan is foiled he begins a campaign to destroy Gotham City...by blowing it up. The Gotham island is evacuated onto two barges...but uh-oh...surprise surprise each barge has a bomb on it and unless one is destroyed the Joker will detonate both...

Those are your general plotpoints.

I can go into more specifics...but won't do so unless asked...cause I know people like to remain ignorant of certain details...