So deeply does The Dark Knight delve into the darkness that lurks in the hearts of men that it comes almost as a shock, bordering on euphoria, to find that it maintains a tenacious grip on hope in the human potential for good.

There is nothing glib or pat about this. The vision of evil is too morbid, the losses too tragic, the moral choices too murky, the heroes too hard-pressed, too compromised. Here is evil as incalculable and remorseless as Javier Bardem’s Anton Chigurh in No Country for Old Men, as capricious as Russell Crowe’s Ben Wade in 3:10 to Yuma.

I have described those earlier films as nihilistic, and the same word has been used by a number of critics, both positively and negatively, to describe The Dark Knight. This is a mistake. The Dark Knight is darker than its predecessor — but something else is here, beyond the calculations of men like Chigurh and Wade. Nihilism gets a hearing but does not carry the day.

Three years ago, Christopher Nolan’s brilliant Batman Begins offered a vigorous and satisfying new reading of who Batman is and what he stands for. It was and is one of the best super-hero movies ever made, though I noted in my review that Nolan was evidently pacing himself, laying the groundwork for something grander.

Was he ever. The Dark Knight goes beyond Batman Begins as only a sequel can do, building on the original, in a way earning comparisons to the grandest of sequels, The Godfather II and The Empire Strikes Back. Though apt, the comparisons are in a way superfluous; the immense ambition and singular achievement of The Dark Knight can’t be reduced to a name-checking sound bite.

The shadow of 9/11 and the war on terror, subtle but distinct in Batman Begins, lengthens and deepens here. Then, the enemy was a fanatical shadow organization dedicated to the destruction of decadent society and ruthless in its tactics (decapitation, weapons of mass destruction). The Dark Knight plunges us into a terrifying world in which an incomprehensibly evil enemy has blown away all semblance of rules while those we look to protect us scramble to catch up. They hold the risk of failure in one hand and the temptation to corruption in the other.

One side, at least, is supposed to believe in rules.

In the old days, even the bad guys believed in rules of some sort. “Criminals used to believe in things,” blusters a dying mob banker in the brutal opening heist scene. “Honor. Respect!” That was then. Today belongs to the Joker. Played with insinuating caprice by the late Heath Ledger, he’s a soulless sociopath with no motivation but to subvert the dominant moral paradigm, to unmask the chaos and meaninglessness of men’s lives and the rules they imagine themselves to live by.

Who or what is the Joker, with his white greasepaint and disturbing scars stretching from the corners of his mouth across his cheeks? “An agent of chaos,” he says grandly at one point, elsewhere dismissing himself as “a dog chasing cars … I wouldn’t know what to do with one if I caught it.”

The filmmakers ultimately make no attempt to explain the Joker. Perhaps no explanation is possible. “Some men don’t want anything logical,” observes Alfred (Michael Caine). “They can’t be bought, bullied or reasoned with. Some men just want to watch the world burn.”

How does one combat such evil? Three heroes represent three possible approaches. First, there’s the Dark Knight (Christian Bale), a grim pragmatist who has learned to do what is necessary, though he sincerely hopes for a day when his methods won’t be needed. He hasn’t given up hope for a normal life as Bruce Wayne, possibly involving lifelong friend Rachel Dawes (Maggie Gyllenhaal, gracefully taking over for Katie Holmes), who knows his secret.

Bruce’s best hope for retirement may be Gotham’s “white knight,” district attorney Harvey Dent (Aaron Eckhart), though Dent is also Bruce’s only rival for Rachel’s affections. A righteous crusader whose campaign slogan is “I Believe in Harvey Dent,” his moral certitude is slyly symbolized by his habit of pretending to toss a coin over decisions where, in fact, the outcome is not in doubt.

Partially bridging the gap between Gotham’s two knights is Lt. James Gordon (Gary Oldman), a dogged, good cop who’s in it for the long haul, and is willing to work with knights of either persuasion, though he won’t pin all his hopes on either.

The Joker poses a string of dreadful dilemmas in order to show up the other side’s rule-bound pretensions as self-deceiving poses: “When the chips are down, these civilized people … will eat each other. You’ll see. I’ll show ya.”

Although there’s one line Batman won’t cross — he won’t kill — he does cross others. Terrible, even impossible choices abound. What rules there are seem unclear, sometimes with tragic consequences.

Yet, amid this virtual symphony of ambiguity and darkness are ringing notes of grace and redemption. With an immersive, fully-realized world, stunningly-choreographed set pieces, lucid dialogue and persuasively-drawn characters, The Dark Knight offers a bleak milieu punctuated by hopeful, even inspiring moments and choices.

Heroes may not be untarnished, but heroism is still possible. Good guys may bend or break the rules, but they may also be willing to fall on their swords for the greater good, to take a hit for something they believe in. Even when all seems lost, people may still do the right thing, taking their last recourse in prayer rather than in Nietzschean ruthlessness. It may be a mistake to believe in Harvey Dent. But I want to believe in the best of The Dark Knight — and back that against the darkness.

Steven D. Greydanus is editor and

chief critic of DecentFilms.com.