It's NOT Joker. It's a henchman, whom the Joker hangs from a high-rise building, as a cold-hearted message to Dent and Batman.
I HIGHLY suggest you don't read the following, if you don't want to be spoiled. I cannot claim accuracy -
DON'T READ IF YOU DON'T WANT TO BE SPOILED
· Wayne Manor is being rebuilt; Bruce Wayne and Alfred are staying in a penthouse suite. Underneath the suite there is a garage where Batman keeps the tumbler, his suit and equipment and a computer terminal.
· Joker is the main villain. One of his first scenes in the movie is a bank robbery where he and his goons wear clown masks. The Bank Manager (played by William Fichtner) tries to stop the thugs, but is stopped by the Joker, who also kills his goons during the robbery as well. He escapes on a carjacked school bus.
· Harvey Dent (Aaron Eckhart) is the new District Attorney. He is possibly dating Rachel Dawes.
· Bruce Wayne is up to his playboy millionaire antics. At one point he throws a party on his private yacht for the cast of an Opera, closing the show for the night.
· Sal Maroni (Eric Roberts) is the new head of the Falcone family. There are gang wars ensuing the streets of Gotham City including Maroni’s gang, and a gang lead by a man named Gambol (Michael Jai White).
· There are Vigilantes, disguising themselves as Batman, patrolling the streets of Gotham. They attempt to break up a confrontation between a Chechen gang and Scarecrow early on in the movie. The Chechens release attack dogs on the Vigilantes, who must be rescued by the Batman.
· Dent wants to end the gang wars in Gotham and put an end to organized crime. To mount a case against Maroni he needs to bring an extradited accountant from Hong Kong named Lau (Chin Han), who has connections with Maroni to Gotham. Batman travels to Hong Kong (as Bruce Wayne) with Lucius Fox in order to bring Lau to Gotham.
· The Joker is somehow approached by the mobs entreating him to cause chaos in Gotham, distracting the cops and Dent from their warfare.
· The Joker does indeed cause chaos in Gotham City. He (in no particular order) kills cops, blows up a hospital (while disguised as a female nurse), and commits other actions causing a general state of fear in the city.
The Joker dies his hair green and wears white make up over his face, never taking it off, causing it to "rot" permenantly onto his face over time.
· At some point, Harvey Dent announces that he is Batman at a press conference.
· Bruce Wayne throws a party for Harvey Dent at his penthouse suite. The Joker and his goons crash it, trying to kill Dent. Batman intervenes, but the Joker ends up kidnapping Rachel, dancing with her at knife point.
· Reese (Joshua Harto), a disgruntled Wayne Enterprises employee, breaks into the applied sciences sector of Wayne Enterprises and somehow discovers Batman’s true identity. He gives this information to a reporter/radio/talk show host named Mike Engel (Anthony Michael Hall), who announces he will reveal the identity on his evening program. Not to be out of the limelight, Joker makes a bomb threat to the TV station, causing the program to be cancelled. Lucius Fox somehow blackmails Reese into not revealing the identity to anyone else.
· Tired of all the vigilantes running around Gotham, and wanting to find the real Batman, Joker kidnaps their leader, a man named Brian Douglas, and hangs him from a flag pole outside the mayor’s office with a Joker card pinned into his chest with a knife. On the card it reads, “Will the real Batman please stand up.” Harvey Dent is making a proclamation of a crime-free 18 months in Gotham to Mayor Anthony Garcia (Nester Carbonell) when the wind blows the dead body into his window.
· Batman/Bruce Wayne is struggling with falling into his persona, and juggling both the life of Batman and Bruce Wayne. He is also seen doing more detective work this time around. He also gets a new suit sometime in the movie.
· Lt. Gordon (Gary Oldman) fakes his own death. His wife, Barbara (Melinda McGraw) is notified about his “death” by Detective Stephens (Keith Szarabajka).
· Joker kills Commissioner Loeb (Colin MacFarlane) and a female judge. At their funeral, the Joker (disguised as a cop) makes an assassination attempt on the mayor.
· At some point, (possibly after the assassination attempt) the Joker and some of his goons are arrested. Batman interrogates the Joker, and ends up beating the snot out of him. The Joker escapes by the use of a bomb planted in the stomach of one of his goons.
· Detective Stephens and Detective Ramirez (Monique Curnen) are cops loyal to Harvey Dent.
· Officer Berg (Matt Shallenberger) tries to kill the Joker, after his wife is killed in the hospital explosion, but is stopped by Gordon.
· There is a chase scene involving the Bat mobile and the Joker in a semi-truck. Joker ends up destroying the Bat mobile/Tumbler, causing Batman to use his Bat-Cycle.
· Eventually Maroni and other gang leaders are rounded up and arrested by Batman, and SWAT squads led by Gordon. Maroni is in a night club with two mistresses (Sarah Jayne Dunn and Kerri Parker) when Batman breaks in and takes him.
· Maroni goes on trial, being prosecuted by Harvey Dent. During the trial, he throws acid (that was smuggled to him by a corrupt cop) in Dent’s face, permanently scarring him.
· The Joker causes so much chaos in Gotham, and makes a threat forcing all of Gotham to evacuate onto huge barges. The criminals and lower class citizens are on one barge, while the Gotham elite are on the other. Joker announces that there are bombs on both barges. The leaders of Gotham must choose to blow up one of the barges, or he will destroy both. This culminates to a showdown between Joker and Batman.
· Dent, now scarred, confronts Maroni. He flips his coin to determine whether to kill Maroni or not. The flip determines that Maroni will live for the time being, but his driver is not so lucky.
· Dent/Two-Face also makes an appearance at a bar, where he kills the cop who supplied Maroni with the acid.
So, basically, 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 plot points.
