This modern-day Batman - Christian Bale reprising his dual role as the costumed hero and Bruce Wayne - is obsessed with the moral need to clean up the corruption that chokes Gotham City.
And the bad guys are feeling the pinch. Gotham's mob bosses, who've allied themselves with a Hong Kong banking whiz (Chin Han) using high-tech accounting systems to launder their ill-gotten gains, are frustrated over Batman's success at cutting into their take.
Enter The Joker (Heath Ledger), a disfigured psychotic with stringy green hair and a fetish for white face-paint and sharp objects, who is neither cowardly nor superstitious. The Joker has an easy answer to the criminals' problem: Kill Batman.
This is the third screen incarnation of the Joker, and the late Ledger's electrifying and much-lauded, performance gives a nod and a wink to both of his predecessors, Caesar Romero and Jack Nicholson, while inhabiting a unique, post 9/11 terrorist head-space.
"I needed someone of extraordinary talent for The Joker," Nolan said of Ledger. "And he was prepared to take on an iconic role and make it his own."
"I think the idea that was most appealing to us about The Joker was that he cuts through the film, that he's elemental," added Jonathan Nolan, the director's brother, who co-wrote the screenplay with "Batman Begins" writer David Goyer.
"It's more frightening because . . . there is no mystery," Jonathan Nolan added. "There is no backstory. He is exactly what he presents himself to be - which is an anarchist."
There is no purpose for the Joker other than to destroy, and he uses copious amounts of C-4 and gasoline to make his point. As Alfred (Michael Caine) says to Batman, "Some men just want to see the world burn."
"The Dark Knight" adds a real-world approach to costumed heroes, addressing the Batman as both a symbol of hope and a cultural icon. One of the film's smarter subplots involves a hero-worshipping copycat Batman, with an ill-fitting cowl and a protective chest plate made from hockey equipment.
The film also brings Bruce Wayne more front-and-center than in previous movie incarnations, and in doing so creates a more believable rich guy than Tony Stark of "Iron Man." It also adds a new, James Bond-ish, secret-agent element to the character. Sipping a cocktail on a yacht full of bikini-clad women in the South China Sea, Gotham's bad-boy billionaire jumps ship and suits up - breaking into a high security Hong Kong office tower. How Sean Connery can you get?
Christopher Nolan is a big fan of the Bond films, and he said that the tone of that movie franchise is evident in both Batman movies.
"[It] gets pushed even further in this film, because of wanting to have the daytime be more threatening," he said. "If Batman rules the night, and The Joker is in the daytime, how does Bruce Wayne deal with that?"
Even Wayne's confidantes have Bond counterparts. Lucius Fox (Morgan Freeman) is Batman's Q, coming up with all sorts of cool gadgets and new vehicles for the crime fighter to use. And Alfred is a breakfast tray-carrying "M," offering advice and advising Batman of the Big Picture. You can even look at The Joker as Dr. No-No.
The Batman and The Joker go toe to toe, but all eyes are on Harvey Dent (Aaron Eckhart), Gotham's charismatic district attorney.
"Harvey Dent is the emotional arc of the story," Christopher Nolan said, and Bruce Wayne sees Dent as the real, long-term answer to Gotham's corruption problems. With Dent waging an open, law-abiding war on corruption, Bruce Wayne can relinquish his role as Batman and finally be with the love of his life, played by Maggie Gyllenhaal (replacing Katie Holmes). But The Joker wants Harvey, too - to show that any man can be turned to the Dark Side.
In the end, the Joker plays both sides against the middle. The conclusion comes down to the flip of a coin.
"The Dark Knight" offers a modern interpretation of the Batman that stays true to 69 years of comic book continuity, in a disturbing and adult morality play that creates the first real costumed hero for our times. *