The key performance in the movie is by the late Heath Ledger, as the Joker. Will he become the first posthumous Oscar winner since Peter Finch? His Joker draws power from the actual inspiration of the character in the silent classic “The Man Who Laughs” (1928). His clown's makeup more sloppy than before, his cackle betraying deep wounds, he seeks revenge, he claims, for the horrible punishment his father exacted on him when he was a child. In one diabolical scheme near the end of the film, he invites two ferry-loads of passengers to blow up the other before they are blown up themselves. Throughout the film, he devises ingenious situations that force Batman (Christian Bale), Commissioner Gordon (Gary Oldman) and District Attorney Harvey Dent (Aaron Eckhart) to make impossible ethical decisions. By the end, the whole moral foundation of the Batman legend is threatened.

Because these actors and others are so powerful, and because the movie does not allow its spectacular special effects to upstage the humans, we’re surprised how deeply the drama affects us. Eckhart does an especially good job as Harvey Dent, whose character is transformed by a horrible fate into a bitter monster. It is customary in a comic book movie to maintain a certain knowing distance from the action, to view everything through a sophisticated screen. “The Dark Knight” slips around those defenses and engages us.

Yes, the special effects are extraordinary. They focus on the expected explosions and catastrophes, and have some superb, elaborate chase scenes. The movie was shot on location in Chicago, but it avoids such familiar landmarks as Marina City, the Wrigley Building or the skyline. Chicagoans will recognize many places, notably La Salle Street and Lower Wacker Drive, but director Nolan is not making a travelogue. He presents the city as a wilderness of skyscrapers, and a key sequence is set in the still-uncompleted Trump Tower. Through these heights, the Batman moves at the end of strong wires, or sometimes actually flies, using his cape as a parasail.