In the ninth episode of its first season, The Leftovers finally depicts the moment that gives the show its title, when 2 percent of the world's population simply vanished in the blink of an eye. Kids at a school science fair stand in a circle, building a circuit to power a light. The camera holds on the smiling face of Tommy Garvey (Chris Zylka), clearly having a great time. The light glows subtly on his face, highlighting his smile.

And then it goes out, something we only see as shadows suddenly cross his face. His expression darkens, too, the smile drifting toward confusion. One of the children in the circle has been taken, breaking the circuit, and no one will ever find out what happened to them.

Some might criticize this sequence for not directly depicting the moment of departure. Some might suggest the show is looking away from its central horror, the unanswerable that drives all of the characters endlessly. But in baldly metaphorical terms, The Leftovers is depicting that central horror. It's showing light turning to dark in an instant, people who thought they knew their universe being rocked.

See, The Leftovers isn't really a show about how 2 percent of the world's population disappeared, or about living through grief. It's not about post-traumatic stress disorder, or even the mysteries at the center of its conceit, really. No, The Leftovers is a show about depression. And it might be the best show on that topic in television history.

How this affects the critical divide over the show

The series, which ends its first season tonight, has become one of the most divisive of the summer, with some critics (including myself) embracing its bold storytelling and sense of surprise. (This is one of the few shows on TV where you never entirely know what you're going to get, once you factor out a constant bleakness.) But others have said that the show is simply too bleak to be any good, that it relentlessly rubs viewers' noses in the characters' misery.

This was not a criticism I understood, really. Intellectually, I could get that most of the events happening on screen were fairly sad, but they were laced with a mordant, gallows humor that popped up at just the right times. Plus, the show had a healthy sense of its own ridiculousness — sometimes too healthy of one (as when it punctuated a pivotal moment in the riveting third episode with Captain and Tenille's "Love Will Keep Us Together").

But in rewatching much of the first season in preparation for this piece and keeping this review by my former AV Club colleague Sonia Saraiya in mind, I found myself realizing how skillful The Leftovers is at forcing you to enter its headspace. Most TV shows meet the viewer halfway, but this one demands you join it in a world of unrelenting sorrow if you're going to get anything out of it. Yes, there are laughs, but to properly "enjoy" The Leftovers is to essentially give yourself over to a worldview that is bottomless and depressive. No matter how well the show punctuates that darkness with the unexpected or with a joke, you can't entirely escape it.

And this is appropriate. Depression is a constant in the lives of those who struggle with it, a monster in the basement that makes its presence known with long scratches on the wall. It's a kind of dark that never goes out, and to live with it is to always feel it lurking, daring you to fall back into it and cut yourself off from the other parts of your life.

This makes it hard to tell stories about depression. When the defining element of a condition is that it makes people not do things, that has a tendency to halt story momentum, which is always about people going out and doing things. The Leftovers gets around this in the grand tradition of genre fiction: it makes the depression completely metaphorical. Those who have Departed aren't just the no-longer-so-physical manifestations of the world that once was. On a symbolic level, they become the parts of the remaining characters that might have made them whole, the pieces depression gobbles whole.

Depression explains so much about the show

Instantly, many of the show's more inexplicable moments — such as, say, a character committing suicide at the end of the eighth episode — snap into place with a crystal clarity. The Departure is no longer an unexplainable thing that has driven some people to distraction. It's that very real monster that everyone is staying only a step ahead of. The show's creators, Damon Lindelof and Tom Perrotta (who also wrote the novel this is based on), have turned the old problem of making stories about depression on its ear. This is now a show about trying to outrun depression, and how exhausting that is.

Even the show's much-derided Guilty Remnant — a cult of people who seem to be slowly trying to erase themselves by never speaking, smoking constantly, and wearing only white — makes much more sense in this context. They are a physical representation of the way depression makes people feel on the inside, stripped of all nuance or meaning, stripped of all self, even, and reduced to a collection of faded beings, disappearing into the surroundings.

But the series' depictions of depression extend beyond these metaphorical ones. The characters themselves brush up against this reality, without ever quite tipping over into saying this is why they act the way they do. One of the last lines of dialogue before the Departure is "I don't know why. I just feel sad," and it plays (particularly in the context of an episode filled with scenes set in a therapist's office) almost as a confession that unlocks the door to something far more terrifying. The world empties of color. Everything changes.

Or consider the ways that the show depicts the characters wrestling with the notion of God. In the show's third episode, a minister (played by the riveting Christopher Eccleston) chases a series of revelations that seem to be divinely inspired. Finally, he's going to have the revelation he requires, the assurance that some divine hand guides him through an uncertain world. But by episode's end, that assurance is yanked away in the cruelest fashion possible. Whatever hope he might have placed in God is ultimately a panacea. All that is left is bleak and cruel and brutal.

How escape seems impossible

But if there's one place The Leftovers excels in portraying the ways depression can warp one's worldview, it's in the scenes where the characters come in contact with people who have either moved past the Departure or ultimately learned to live with it as background noise in their lives. The characters we follow react to these people as if they were space aliens, utterly inconceivable as intelligent beings.

For instance, episode six ends with what amounts to a genuine religious experience for a woman named Nora (Carrie Coon), who lost her entire family on the day of the Departure. She's essentially suicidal, hiring prostitutes to shoot her. She stages things so she doesn't get hurt, but she's perhaps hoping that someday, she'll be able to finally end her existence. Instead, she has her life nearly erased by an impostor who wants to use Nora's name to act as a sort of Departure Truther, and she finds herself in the presence of a man named Holy Wayne, who either knows exactly what to say to someone in their grief and sorrow or really can take those feelings away via a hug.

It's a ridiculous notion, but as played by Coon, it becomes transcendent. This physical contact, this moment of shared, raw pain, is exactly what she needs to begin the healing process. And it's also what The Leftovers needs to consider the difference between situational depression (which almost everyone will experience after a setback or sorrow) and clinical depression (which is the psychological condition). The other characters simply can't believe Nora has moved toward acceptance like this. Nora's boyfriend's daughter even rails that she can't be okay. She must be pretending to be okay.

And it's in that admission that The Leftovers finds a kind of mission statement. It's easy, when trapped in the throes of depression, to simply assume that the entire world around you is exactly the same way. Nora's attitude so baffles the girl not because she can't believe in people moving past grief, but because her own sorrow has become so all-encompassing that she can't imagine any path lit in that darkness.

Granted, that's not going to be everyone's recipe for light-hearted and enjoyable summer TV. The Leftovers, however long it runs, will always be an acquired taste. But to find yourself in its headspace is sometimes intensely illuminating and rewarding. It digs deep, and it refuses to let go. It's ferocious.

But it's also so moving and empathetic, ultimately. It understands that the Departure wasn't just a day when these people lost friends and family, or a day when a light went out. No, the Departure was the day these characters realized that they, too, had been missing all along.