Heads up: a thunderbolt is about to rip into the blanket of bland we call summer movies. The Dark Knight, director Christopher Nolan's absolute stunner of a follow-up to 2005's Batman Begins, is a potent provocation decked out as a comic-book movie. Feverish action? Check. Dazzling spectacle? Check. Devilish fun? Check. But Nolan is just warming up. There's something raw and elemental at work in this artfully imagined universe. Striking out from his Batman origin story, Nolan cuts through to a deeper dimension. Huh? Wha? How can a conflicted guy in a bat suit and a villain with a cracked, painted-on clown smile speak to the essentials of the human condition? Just hang on for a shock to the system. The Dark Knight creates a place where good and evil '” expected to do battle '” decide instead to get it on and dance. "I don't want to kill you," Heath Ledger's psycho Joker tells Christian Bale's stalwart Batman. "You complete me." Don't buy the tease. He means it.

The trouble is that Batman, a.k.a. playboy Bruce Wayne, has had it up to here with being the white knight. He's pissed that the public sees him as a vigilante. He'll leave the hero stuff to district attorney Harvey Dent (Aaron Eckhart) and stop the DA from moving in on Rachel Dawes (feisty Maggie Gyllenhaal, in for sweetie Katie Holmes), the lady love who is Batman's only hope for a normal life.

Everything gleams like sin in Gotham City (cinematographer Wally Pfister shot on location in Chicago, bringing a gritty reality to a cartoon fantasy). And the bad guys seem jazzed by their evildoing. Take the Joker, who treats a stunningly staged bank robbery like his private video game with accomplices in Joker masks, blood spurting and only one winner. Nolan shot this sequence, and three others, for the IMAX screen and with a finesse for choreographing action that rivals Michael Mann's Heat. But it's what's going on inside the Bathead that pulls us in. Bale is electrifying as a fallibly human crusader at war with his own conscience.

I can only speak superlatives of Ledger, who is mad-crazy-blazing brilliant as the Joker. Miles from Jack Nicholson's broadly funny take on the role in Tim Burton's 1989 Batman, Ledger takes the role to the shadows, where even what's comic is hardly a relief. No plastic mask for Ledger; his face is caked with moldy makeup that highlights the red scar of a grin, the grungy hair and the yellowing teeth of a hound fresh out of hell. To the clown prince of crime, a knife is preferable to a gun, the better to "savor the moment."

The deft script, by Nolan and his brother Jonathan, taking note of Bob Kane's original Batman and Frank Miller's bleak rethink, refuses to explain the Joker with pop psychology. Forget Freudian hints about a dad who carved a smile into his son's face with a razor. As the Joker says, "What doesn't kill you makes you stranger."

The Joker represents the last completed role for Ledger, who died in January at 28 before finishing work on Terry Gilliam's The Imaginarium of Doctor Parnassus. It's typical of Ledger's total commitment to films as diverse as Brokeback Mountain and I'm Not There that he does nothing out of vanity or the need to be liked. If there's a movement to get him the first posthumous Oscar since Peter Finch won for 1976's Network, sign me up. Ledger's Joker has no gray areas '” he's all rampaging id. Watch him crash a party and circle Rachel, a woman torn between Bale's Bruce (she knows he's Batman) and Eckhart's DA, another lover she has to share with his civic duty. "Hello, beautiful," says the Joker, sniffing Rachel like a feral beast. He's right when he compares himself to a dog chasing a car: The chase is all. The Joker's sadism is limitless, and the masochistic delight he takes in being punched and bloodied to a pulp would shame the Marquis de Sade. "I choose chaos," says the Joker, and those words sum up what's at stake in The Dark Knight.

The Joker wants Batman to choose chaos as well. He knows humanity is what you lose while you're busy making plans to gain power. Every actor brings his A game to show the lure of the dark side. Michael Caine purrs with sarcastic wit as Bruce's butler, Alfred, who harbors a secret that could crush his boss's spirit. Morgan Freeman radiates tough wisdom as Lucius Fox, the scientist who designs those wonderful toys '” wait till you get a load of the Batpod '” but who finds his own standards being compromised. Gary Oldman is so skilled that he makes virtue exciting as Jim Gordon, the ultimate good cop and as such a prime target for the Joker. As Harvey tells the Caped Crusader, "You either die a hero or you live long enough to see yourself become a villain." Eckhart earns major props for scarily and movingly portraying the DA's transformation into the dreaded Harvey Two-Face, an event sparked by the brutal murder of a major character.

No fair giving away the mysteries of The Dark Knight. It's enough to marvel at the way Nolan '” a world-class filmmaker, be it Memento, Insomnia or The Prestige '” brings pop escapism whisper-close to enduring art. It's enough to watch Bale chillingly render Batman as a lost warrior, evoking Al Pacino in The Godfather II in his delusion and desolation. It's enough to see Ledger conjure up the anarchy of the Sex Pistols and A Clockwork Orange as he creates a Joker for the ages. Go ahead, bitch about the movie being too long, at two and a half hours, for short attention spans (it is), too somber for the Hulk crowd (it is), too smart for its own good (it isn't). The haunting and visionary Dark Knight soars on the wings of untamed imagination. It's full of surprises you don't see coming. And just try to get it out of your dreams.