The Dark Knight’s only redeemable character is the criminal who saves the ferries

“The battle for Gotham’s soul.”

That’s how The Dark Knight’s Joker, dangling over the city, finally in Batman’s clutches, describes the havoc he’s wreaked. It could very well be the subtitle of the movie, about a crime-ridden city with obfuscated heroes, who are put through moral ringers at the behest of a clownish chaos agent. The Joker — a mysterious man with an unclear backstory, who’s latched himself onto a mob syndicate to fund a series of twisted, grandiose social experiments — wants to prove that the rotten core of Gotham is a product of its citizens. As he says earlier in the film, “their morals, their code, it’s a bad joke. Dropped at the first sign of trouble. They’re only as good as the world allows them to be.”

That thinking generates the Joker’s largest experiment, loosely based on the “Prisoner’s Dilemma,” a fundamental scenario in the study of game theory. He rigs two ferry boats leaving the city with explosives, and gives the passengers on each boat the trigger for the other. One boat contains average civilians, but the other contains prisoners, and therein lies the moral quandary; he informs them that one of the boats must blow up the other before midnight, or he’ll detonate both, killing them all. The Joker assumes it’s inevitable that one of the boats will blow up the other, because he believes that most people are like him: only out for themselves.

Instead, the boat sequence steers the nihilistic story of The Dark Knight toward a somewhat happy ending. Not happy in circumstance, necessarily, but happy in that it posits humanity as more than just self-servicing blight on the planet. Though it looks, for a moment, like the passengers will turn on another, a prisoner, played by actor Tom Lister, takes the detonator from the prison warden and throws it out the window. He doesn’t flinch or think it over for a moment, only telling the warden before throwing it, “I’ll do what you should’ve did 10 minutes ago.” Likewise, a civilian on the other boat who was about to pull the trigger decides against it. As Batman tells the Joker, “This city just proved that it’s full of people ready to believe in good.”

The prisoner’s act is significant because of its simplicity. With a single choice, he rejects the Joker’s primal ideology — no game theory charts required — and unfurls what he spent a whole movie trying to prove. Harvey Dent is beaten down by the Joker to the point that he becomes a villain himself, almost proving the Joker’s point. The prisoner makes a basic sacrifice that demonstrates the inherent goodness of even the would-be “worst” people. He proves that morality doesn’t have a dividing line, something even Bruce Wayne struggles to understand.

Many have surmised that The Dark Knight is an allegory for the Bush administration’s War on Terror, a theory punctuated in a 2008 piece by Ron Briley for George Washington University’s History News Network, where he posits that “the film’s politics seem to suggest that Americans want to maintain the myth of national innocence but secretly acknowledge that the extralegal excesses of the Bush administration may be necessary to fight evil.”

Indeed, The Dark Knight shows the cost of maintaining a visage of incorruptibility by placing “heroes” in compromising situations that provoke their principles. Bruce, for instance, uses intrusive tech to track the Joker, a “for the greater good” act that, though effective, questions his ethos as a makeshift protector.

Then there’s Dent, whose girlfriend Rachel was killed by the Joker, which sends him spiraling down his own killing spree, utterly undone by the system he worked so hard to protect. Dent blames Commissioner Gordon for playing into the Joker’s trap, which he did, to the detriment of his city. All of these heroic characters are belayed with the burden of expectation, of holding title, along with law and order. They don’t always do the right thing. They lose those around them — and a bit of themselves, too. It takes a great deal to combat terror, which is relentless and unpredictable by nature.

That’s why the prisoner’s sacrifice stands out. It’s different than the civilian’s decision not to pull the trigger, because it’s neither burdened nor overthought. It’s the purest possible act of good, from the least likely source, and its an act that indirectly leads to the film’s conclusion and to the end of Batman’s arc in The Dark Knight. Though Bruce never lost hope that people would ultimately do the right thing, the boat act helps him wield the power of sacrifice. He makes an equally unburdened choice in the end: he takes the fall for Harvey Dent’s crimes, so that Gotham’s faith in lawful protection remains unmarred, and so the Joker’s capture feels like a win, not a compromise.

By the time the credits roll, it wasn’t the Joker or Batman who won the “battle for Gotham’s soul.” It was Gotham itself, and the good people who live there, who thwarted terror by simply rejecting it. That sends a cutting message, and is in part why the themes of The Dark Knight feel pertinent still, as our police carry out morally questionable deeds, as our campaigns are corrupted by outside forces, but as our civilians counteract chaos and hate with small acts of kindness. The prisoner on the boat is a token of that greater ideal, and he’s the true hero of The Dark Knight —not because he’s a superhero, but because he’s not.

Lindsey Romain is a pop culture writer living in Austin. Follow her on Twitter @lindseyromain.