There's one big question at the core of writer-director M. Night Shyamalan's new movie Glass: Who gets to be a hero? In the real world, a hero can be anybody. Someone who does the Heimlich maneuver in a diner, a firefighter, Colin Kaepernick. In movies (and TV and books and comics), though, the people folks call heroes tend to wear capes and have supernatural abilities. They may have started out as average citizens, but through some otherworldly power or scientific experiment, they've become more than human. Their heroism comes from their abilities. But in Shyamalan's world, these two types of heroes—or villains, or both—are indistinguishable. And that's what makes them great.

It all started with Unbreakable, a comic-book-inspired movie Shyamalan pretty much had to beg studios to produce back in 2000. In that film, David Dunn (Bruce Willis) discovered he had the uncanny ability to survive almost anything, while Elijah Price/Mr. Glass (Samuel L. Jackson) suffered from a condition where almost anything could break him, so he used his brain to become an evil mastermind. Fans loved it at the time, but Shyamalan moved on to movies like The Village and Lady in the Water, and it seemed like he might never return to that world again.

Then, in 2016, he released Split, a movie about a man (James McAvoy, doing the most in the best possible way) who had 20-plus personalities, one of which possessed superhuman strength and abilities. It wasn't advertised as an Unbreakable sequel, but there at the end was David Dunn, setting up Glass, a movie that would complete the most unlikely "superhero" trilogy ever. Unlikely because it comes from Shyamalan and not Marvel or DC, and unlikely because its protagonists and antagonists are real people who live in Philly rather than Gotham, and there isn't an Infinity Stone in sight.

"It goes hand-in-hand with my attempt in my movies to ground everything," Shyamalan says. "To ground the supernatural, and in this case the comic book world—or at least the concepts of that world—in a way that starts to make us wonder whether a percentage of what I'm depicting is actually true."

Glass exists in percentages that just might be real. Set nearly two decades after the events in Unbreakable and a short time after those in Split, it finds Dunn working at a store that sells security systems and side-hustling as a vigilante known as the Overseer. McAvoy's Kevin Wendell Crumb/the Beast is haunting Philadelphia and kidnapping and murdering young women, and Mr. Glass has been institutionalized under the care of Dr. Ellie Staple (Sarah Paulson), who seeks to treat people with a particular delusion of grandeur that makes them believe they have superhuman powers. When Dunn and Crumb come under her care as well, she finds herself with three very different subjects to observe—and Mr. Glass finds himself two potential accomplices in his scheme to show the world just how real self-manifested superpowers truly are.

[#video: https://www.youtube.com/embed/Q7ztHi9ejp4

But here's the thing: Are they real? Moreover, what is "real" really? If someone believes they have superpowers that aren't there, does that matter if they can still bend steel and climb walls? Or, to use the analogy Shyamalan gave me, does it matter if a pill is a placebo if it still makes you feel better? The patients in Staple's care are being treated because it seems insane to think that anyone could will themselves to withstand a train crash, as Dunn did in Unbreakable. What they're doing, as Shyamalan explains, is "hobbling together from the ordinary something extraordinary." But if they're still able to do good—or evil—in the world, does their implausibility matter? Are they the mentally ill ones, or is it everyone else who can't see their capabilities? Who gets to call themselves a hero?