The summer of the superhero continues unabated with the arrival of “The Dark Knight,” the second installment in director Christopher Nolan’s highly praised reboot of the Warner Bros. and DC Comics Batman franchise. As in “Batman Begins,” Christian Bale returns as both Gotham City’s masked avenger and his daytime alter ego, “millionaire philanthropist Bruce Wayne,” as the character was designated on the 1960s campy TV serial version.

The film energetically picks up where its predecessor left off, with Gotham City’s underworld attempting to stave off extinction at the hands of a formerly complacent populace goaded into action by Batman’s crime-fighting example. But at the same time that Batman aids a police lieutenant, James Gordon (Gary Oldman), and a firebrand district attorney, Harvey Dent (Aaron Eckhart), he inspires a new breed of criminal. In what is simultaneously one of the most energetic yet exposition-heavy action sequences in recent memory, an archfiend identified as the Joker (the late Heath Ledger, in his final role) performs a daring bank robbery that soundly trounces the concept of honor among thieves and pushes the film’s body count into the double digits within its first five minutes.

“What doesn’t kill you simply makes you stranger,” the Joker opines in a peculiarly magnetic nasal purr. The film’s plot — involving Asian money laundering, a Mafia power grab, and a love triangle among Rachel Dawes (Maggie Gyllenhaal, replacing Katie Holmes from the first film), Wayne, and Dent — gradually becomes a strange, conceptually muscle-bound thing indeed.

“Batman Begins” packed both standard multiplexes and IMAX theaters for much of the summer of 2005, and in the spirit of bigger-is-better, “The Dark Knight” will also be presented in the large-negative spectacle format. For this outing, Mr. Nolan and his crew have photographed six different action sequences using IMAX cameras, rather than relying on the standard practice of optically expanding a standard negative to a six-story-high projectable size.

Perhaps in keeping with this increase in height, “The Dark Knight” script contends with some lofty ideas. By the midpoint of the nearly two-and-a-half-hour proceedings, the characters have begun to assail one another with so much moralistic, and oddly artificial, speechifying about choice, heroes, and truth that the film begins to resemble an action-blockbuster version of Brecht’s “Mother Courage.”

“The night is darkest before the dawn,” D.A. Dent reminds a roomful of reporters, prior to undergoing a transformation that will come as no surprise to those familiar with the Batman comic books, “and I promise you the dawn is coming.” Yes, but not before at least a half-dozen more warehouse explosions, hostage crises, building plunges, and unavoidable personal calamities doled out with such frequency and perfunctory expertise that they cease to have much dramatic impact.

Tragically, “The Dark Knight” comes most alive not when the IMAX camera blows the outside of the frame up as the filmmakers explode everything within, but whenever Heath Ledger is on screen. Peevishly and distractedly licking the inside of his macabrely scarred mouth, and exulting in mass murder with the same giddy sociopathic pleasure with which he delivers petty cruelty, Ledger’s Joker effortlessly surpasses Jack Nicholson’s performance in the same role in Tim Burton’s 1989 “Batman.”

Unfortunately, the movie as a whole doesn’t dig as deeply into the grotesque with the same gusto. Ledger steals the show by meeting the audience’s prurient escapist expectations at an honestly malevolent level, to which the film’s otherwise rather humorless and joyless script parsimoniously refuses to stoop. Rarely has a film been so ill-served by scrupulously sticking to a box-office-friendly PG-13 rating. Everyone talks a good game about human maliciousness and moral rot at its most foul, but despite all the bangs, booms, swoops, and crashes, except when Ledger is on screen, it feels mostly like talk.

Ledger’s Joker has such wicked charisma that, as his character becomes a kind of collective urban id, the movie itself starts to fall behind and the emotional climax of the story arrives a full half-hour before the actual showdown between hero and villain. It’s a solo turn in which the Joker exits a booby-trapped building, and the scene is not so much notable for the pyrotechnics or even for the fact that Ledger plays it dressed in a nurse’s uniform, but for the fact that late actor makes his character seem so gloriously alive and real amid all the shadowy high-budget digital tinsel. It’s a moment of such vivid unrepentant malice that for a moment it’s possible to forget that it is itself a swan song and a coda to a career and a life ended far too soon.