Every week, we pick a new episode of the week. It could be good. It could be bad. It will always be interesting. You can read the archives here. The episode of the week for January 21 through 27 is “Vaulting Ambition,” the 12th episode of the first season of CBS All Access’s Star Trek: Discovery.

What is Star Trek?

That question has dogged Star Trek: Discovery — the first new Star Trek TV series since Enterprise closed up shop in 2005 — since it began. The show’s darker tone and consideration of the difficulties of building and maintaining utopia seemed to be firmly at odds with the franchise as a whole, which has famously posited a future in which humanity is a peaceful species, exploring the cosmos and constantly striving to build a better universe.

Discovery is dark. It’s occasionally pessimistic. In the pilot, several of its characters more or less commit war crimes. The show has spent much of its season with the United Federation of Planets fighting the Klingons, and it has argued forcefully several times that the ends justify the means — an idea that, to put it mildly, would seem to cut against the philosophy of Star Trek. (On the micro level, though, Star Trek has never been all that consistent when it comes to its ideals.)

Indeed, the simultaneous presence of The Orville, Fox’s more forthrightly optimistic Star Trek: The Next Generation homage starring Seth MacFarlane, has spurred a debate in some circles of the internet: Which series better captures the “real” spirit of Star Trek?

My usual contribution to these debates is to declare that Star Trek is whatever we say it is, but that tends to make people unhappy. So instead, I’ll advance the argument that Star Trek is an essentially hopeful story about what it would mean to build a better world. That has been more or less true across all of the franchise’s TV series, movies, and assorted other products.

It’s true of Star Trek: Discovery, too, as the series’ most recent story arc hammers home.

As the idea of “hope” changes in our world, it changes in Star Trek’s world, too

Star Trek’s optimism undergoes fundamental shifts, depending on which iteration of the franchise you’re looking at. The overriding principle of the original 1960s TV series was that hope stems from humanity overcoming its differences, so the bridge of the USS Enterprise included people of all races and even a Soviet.

The 1987-born Star Trek: The Next Generation, arriving in a more conservative political climate, sometimes seemed almost wistful for Gene Roddenberry’s original dream of a more progressive future. (For a show set in the future, it’s weirdly nostalgic.) Deep Space Nine, which debuted in 1993, asks whether this sort of galactic multiculturalism is even possible in a setting where the characters can’t fly away in their spaceship at the end of every episode.

Optimism and hope for a better future shift as our times shift. Some periods of history lend themselves well to full-throated, brightly colored adventures, while others are better suited to darker deconstructions. Star Trek has and can encompass both tones, so long as it prescribes that humanity must strive to be better.

Thus, it makes sense that Discovery would be darker, even, than Deep Space Nine or the misbegotten Enterprise (which was kinda sorta a War on Terror allegory at times). It takes place both in a dark era within the Star Trek timeline — roughly a decade before the events of the 1960s series — and in our own reality.

It’s easy to become convinced that what light is left in the Discovery universe emerged from a dying star, not from something being newly born. Discovery is a show about how you hold fast to your ideals when you don’t know whether tomorrow is coming.

The “not my Star Trek” arguments against Discovery, then, have always struck me as a little silly. The characters on the show might be tempted, and they might occasionally screw up. But they always, always find some way to return to the optimism of Starfleet and the Federation.

Contrast this with The Orville, which retreats, constantly, toward the past, whether in its blatant Next Generation homages or its humor centered on 20th-century pop culture — it’s not a show about a better future, but about some memory of a better future that we left in the past and need to reclaim. Like so much modern entertainment, it is poisoned by nostalgia.

Contrast this with Discovery’s genuine weight and moral intrigue; this new Star Trek could devolve into dry philosophical discussion but for the strength of its characters. Especially its protagonist, the mutineer–turned–unlikely beacon of hope, Michael Burnham (Sonequa Martin-Green). The series needed to push Michael down as low as it could in its early going, to help her understand just how much her ideals meant to her.

All of these qualities of the show are thrown into sharp relief by its latest storyline, which I’m about to spoil completely, so before you read on, you’d better be okay with learning about a bunch of big twists.

Discovery has found a new gear by hanging out in Star Trek’s famed “Mirror Universe”

CBS split the first season of Discovery into two batches of episodes, with nine airing in the fall of 2017 and six airing in the winter of 2018. When the first half of the season ended, it did so on a cliffhanger that deposited the USS Discovery in a corner of space no one had ever seen before.

That corner of space turned out to be the “Mirror Universe,” a famed, occasionally visited Star Trek locale where humanity evolved not into a peacefully progressive species of space-farers, but into a brutally authoritarian species known for hunting down other alien races, who have banded together to resist the “Terrans.”

Almost as soon as Discovery’s characters were stranded in the “Mirror Universe,” the show began unleashing a long series of twists. Throughout the second half of the season, some characters die, while others are lost in a kind of hallucinatory dreamscape and must try to find their way back to reality. Michael’s love interest, Ash Tyler (Shazad Latif), is revealed to be the Klingon warrior Voq (who haunted the season’s first handful of episodes), modified to appear human.

In “Vaulting Ambition,” the Discovery’s captain, Gabriel Lorca (Jason Isaacs), is revealed not just to be from the Mirror Universe but someone who came to the prime Star Trek universe specifically to find Michael. He wants to bring her back to the Mirror Universe, where he’s been “grooming” the Mirror Universe version of Michael since her childhood. (The episode does not specify for what, but the heavy implication is sexual abuse.)

These twists do much to destabilize whatever status quo Discovery had built up, and they’ve better crystallized the ideas at the heart of the show, too. Michael pretends to be the harsher, harder, more ruthless Mirror Michael, to gain the trust of other Mirror Universe inhabitants who have information about how to get back to her universe. But she worries constantly she is losing some part of herself in the process.

The alien character Saru (Doug Jones) now finds himself in a place where his species is hunted for food. The Discovery’s science officer, Paul Stamets (Anthony Rapp), becomes lost in a strange other world built by spores, where he has to figure out how to get back to reality with the help of his Mirror doppelganger. And Ash struggles to reconcile his humanity and love for Michael with the Klingon memories suddenly taking up residence in his mind.

Lorca suffers endless amounts of torture just to get closer to the emperor he would depose in a coup (which unfolded at some unspecified point before the series began, but which he intends to revive now that he’s back in the Mirror Universe).

But only he feels as if he is single-minded, rather than exploring the chasm within. He thinks he knows what’s his, and he’s relentless in his pursuit of it. (In this sense, the Mirror Universe arc makes a surprisingly suitable companion to Black Mirror’s season four Star Trek riff “USS Callister.”)

The divide between our best and worst selves, then, is the core of Discovery. The utopian future of Star Trek is not preordained. Even those who live within it can find that it’s far too easy to slip into authoritarian modes of thinking when exposed to them for too long. There are no guarantees in this world, only things worth fighting for.

Hope isn’t something fragile that you cup carefully in your hand to bar it from escape. It’s just over the horizon, over there, and to reach it, you’re going to have to pursue it endlessly and pray you have the strength to find it. It’s the pursuit that makes it worth it, the means and not the ends.

Star Trek: Discovery is available on CBS All Access in the US. (Yes, I know. Booooo, hisssss.) It’s on the Space Channel in Canada and on Netflix in all other non-US, non-Canadian countries with Netflix.