At the core of many a good drama is the relationship between protagonist and antagonist. This being 2008, we’re living in a world that’s way beyond the white hat/black hat days of yore, when a scowl or choice of headgear would identify which side you were on. No, things are way more complex now, and that complexity is at the heart of The Dark Knight, and makes it a very special film indeed.

Christopher Nolan’s first outing with Batman was largely successful, but the story became more of a generic action thriller towards the end. This time round, the story is firmly rooted in the psyches of two characters who are poles apart: Batman and The Joker. Batman lives in a world of absolutes, hoping that his example can help turn the tide of evil in Gotham, and seeing in legal crusader Harvey Dent a populist whose success within the justice system may allow Batman to hang up his cape.

That analysis only works if you believe Batman really is capable of relinquishing his identity though, and one person who’s sceptical about that is The Joker. A poster child for the post-Columbine generation, The Joker has chosen to embrace chaos as the best response to the world he’s been brought up in. Every time he gets the chance to talk about his past, a different ‘origin’ story emerges from his mouth, empty as the tales of suffering and rebirth on Oprah that he’s grown up watching. Never mind what people tell you they’re like: what interests The Joker is how they really are, and to that end he sets up a series of deadly scenarios around Gotham that test its citizens, its police, and its caped crusader. There’s no winning any of The Joker’s games: they’re pretty much guaranteed to cause death and destruction, the only distinction being exactly how the situations play out, and what that tells him about human nature.

This being Gotham, human nature tends towards the bleak. Even love is no guarantee of freeing yourself from the all-pervading corruption of the city, as the fate of Harvey Dent and his love Rachel - also involved in a triangle with Bruce Wayne, Batman’s alter ego - demonstrates. And if Venus will not win through, it’s left to the forces of warlike Mars and stern Jupiter to fight it out in the streets of the city.

And if all of that sounds epic and dark, you’d be right. This is cinema for adults who are willing to tackle big questions about ethics and morality. Sure, it also delivers astonishing action sequences, fabulous gadgets, and world class acting, but really this is a film that should leave you feeling uncomfortable by the time it finishes. If all you’re left with is adrenaline, then you got the booby prize basically.

All the actors deliver the goods, though I’m still not convinced by Christian Bale’s impossibly deep Batman voice, but towering above them all is Heath Ledger’s take on The Joker. Previously a part owned by Jack Nicholson, Ledger indelibly stamps his mark on the role in the same way that Nirvana’s Smells Like Teen Spirit trumped Led Zeppelin’s take on rock and roll: both classic performances, and each attuned to their times.

While Marvel’s slate of superhero films could have been made pretty much anywhen, the only contemporary aspect being the CGI, The Dark Knight is absolutely a product of its times in ways that run deeper than how the effects are done. One argument I’ve heard that’s pretty convincing is that this take on Batman is about how America sees itself in the world today: wanting both to be powerful and popular, turning to extreme measures in the face of its failure to deal with terrorism, wanting to continue to use democratic methods but increasingly subverting them when they’re inconvenient. There’s a lot to be said for that perspective, and getting that kind of mileage out of a superhero film is quite an achievement.