Warning: Serenity spoilers ahead. You may want to bookmark this for later if you haven't seen the film yet.

Joss Whedon, the man behind Buffy the Vampire Slayer and Angel, has a knack for creating TV shows with cult followings, and his sci-fi western Firefly was no exception. The show, which followed an eclectic band of outlaws aboard the 26th century smuggling ship Serenity, was cancelled by Fox in 2002 after only 11 of 14 episodes produced had aired, but an intense core of fans—and bootlegged episodes circulating on peer-to-peer networks—continued to spread Firefly's evangel. When the series was released on DVD, it became a surprise hit: big enough to convince Universal to back a feature film follow-up, Serenity, which opens this weekend.

The interesting thing about Firefly's cult following, though, is that it seems to include a disproportionate number of libertarians. At an advance screening in Washington, D.C., I counted the head of Bureaucrash, a couple of folks from the Cato Institute, and at least a half-dozen from the Institute for Humane Studies.

It's not hard to see why. The entrepreneurial Captain Mal Reynolds (Nathan Fillion) and First Mate Zoë Washburn (Gina Torres)—who's married to pilot Wash (Alan Tudyk)—are veterans of a failed war of independence against The Alliance, the series' main heavies. Ship medic Simon Tam (Sean Maher) is a fugitive who abandoned a lucrative medical career on the core planets to break his brilliant teenaged sister River (Summer Glau) out of an Alliance facility where her high-octane brain was being folded, spindled, and mutilated for mysterious purposes. There's sexual tension so thick it might drip on you between Mal and Inara Serra (Morena Baccarin), a "registered companion," which is Firefly-speak for a high-class (and high-status) licensed prostitute. And Second Amendment buffs have a kindred spirit in mercenary muscleman Jayne Cobb (Adam Baldwin). As Whedon himself puts it, "Mal is, if not a Republican, certainly a libertarian; he's certainly a less-government kinda guy. He's the opposite of me in many ways."

For those who think a bit more like Mal, there's plenty of red meat in Serenity from the very outset. The backstory is quickly provided by a scene at an Alliance school, where a teacher sadly muses that it's hard to understand why the benighted Independents, the secessionists, have resisted the attempt to bring them the gifts of civilization. A young, pre–brain tampering River Tam knows:

We meddle... People don't like to be meddled with. We tell them what to do, what to think, don't run, don't walk. We're in their homes and in their heads, and we haven't the right. We're meddlesome.

And, as it turns out, they are. The action of the early second act is driven by the Serenity crew's attempt to discover what, exactly has been done to River—and decide whether the Alliance's fiddling has rendered her too dangerous to have aboard—while evading the agent sent to track her down, a man known only as The Operative (Chiwetel Ejiofor).

Matters are complicated when the crew discover why the Alliance is so eager to retrieve their experiment: She has information about a horribly failed plan to develop a soma-like air additive called "pax," meant to render populations docile. It works too well: Millions of people in a test population on a hidden planet simply gave up on living. As a handy expository hologram-recording by one of the scientists involved tearfully explains, "We meant it for the best, to make people safer." And in a slight—but crucial—departure from the series, it is made clear that this is not merely the work of "the Alliance" as such, but of the Parliament: A democracy did this. Mal and company resolve to expose the experiment, convinced that despite the tragic results, eventually "They'll swing back to the belief that they can make people better. And I don't hold to that."

The most important source of ideas in Serenity, though, is not a kind of vague libertarianism, but existentialism. As Whedon explains in director's commentary for the Firefly episode "Objects in Space," he was influenced at a young age by philosopher Jean-Paul Sartre's novel Nausea, the themes of which permeate that episode.

Whedon has a gift for integrating existentialist ideas seamlessly into his scripts. One of Sartre's central ideas, for example, is that of "bad faith," the attempt to deny our own agency and responsibility. Among his classic illustrations is that of the café waiter who wishes to vanish into his role, not merely be a person who happens to work at a restaurant, but to become "a waiter." And in "Objects in Space," that idea is concisely inserted in an exchange between River and the ruthless but oddly philosophical bounty hunter Jubal Early (Richard Brooks):

River: You hurt people.

Early: Only when the job requires it.

River: Wrong. You're a bad liar. [...] You like to hurt folk.

Early: It's part of the job.

River: It's why you took the job.

In Serenity, however, the central influence appears to be not Sartre but Albert Camus. The Operative, for example, is emphatically not some mere bounty hunter, but a true believer. As he explains at one point, "I believe in something greater than myself: A better world, a world without sin." He has no illusions, either, about the morally monstrous acts he must perpetuate in service of that end, acts he recognizes make him unfit to live in his own utopia. The Operative is a Moses who knows he will not reach the promised land he hopes to help make. He is, in other words, a perfect instance of the revolutionary mindset Camus describes in The Rebel, an anti-Marxist essay that was the catalyst for Camus' break with the (then) pro-Soviet Sartre. For the revolutionary, Camus notes, values are "only to be found at the end of history. Until then there is no suitable criterion on which to base a judgement of value. One must act and live in terms of the future. All morality becomes provisional."

Camus, though, distinguishes between the revolutionary, who dreams of imposing a totalizing new world order, and the rebel, who has the narrower goal of defending his own dignity in the face of oppression. Mal, it's made clear, is the latter: When The Operative tells him that he can't hope to beat The Alliance, Mal responds, "I got no need to beat you; just want to go on my way." For Camus' rebel, though, that recognition that there is something in oneself worth fighting for, a taste for freedom worth defending, metastasizes into a realization that everyone shares the same dignity and rights—even, perhaps, the oppressor. That move from the personal to the political gives the cynical Mal a renewed sense of purpose, something to believe in—which is another of Serenity's central themes.

The idea at the core of Camus' The Myth of Sisyphus is what the author calls "the absurd": Human beings are driven to seek greater meaning and purpose in a universe where, for the good and wicked alike, all roads lead to the grave. And Whedon has a powerful absurdist sensibility. As the film's third act begins, just as the crew has apparently escaped a tough situation, a major character delivers a comic line and, just as the audience is beginning to laugh, is abruptly, brutally, pointlessly killed. It is not a noble sacrifice, not a defeat in battle; there are no stirring, poignant last words. Like so many actual deaths, though very few dramatic ones, it is utterly unexpected and serves no purpose—beyond, perhaps unsettling the Whedon-novice's complacent assumption that main characters can't be killed off arbitrarily. The laugh line is, appropriately enough, "I am a leaf on the wind." (It's funny in context.)

In the face of an absurd universe—one lacking transcendent, factory-installed meanings—we are compelled to create our own. After explaining that The Operative is dangerous precisely because he is a "believer," ship's preacher Shepherd Book tells Mal "I don't care what you believe. Just believe," echoing the proto-existentialist theologian Søren Kierkegaard, who stressed the centrality of passionate commitment, "leaps of faith," in religion.

The Alliance's horrific attempt to "make people safer," provides more than a cartoonish portrait of out-of-control government. For, as we learn, it is not merely that the "pax" gas proves lethal: It kills by making those who breathe it indifferent to life. The residents of the experimental planet simply stopped caring about everything, stopped bothering to get out of bed, to work, to eat. They become, in other words, much like extreme versions of the affectless Meursault in Camus' The Stranger.

Of course, you don't have to have read Camus, or even be fond of berets or clove cigarettes, to be a fan of Serenity. The film's genius is that it works on so many levels—political, philosophical, and (not least) narrative. If you show up in theaters just looking for a tightly plotted, smartly scripted sci-fi action flick, you'll come away happy. For the attentive viewer, though, Serenity is not just a string of good chase scenes, but an "absurd reasoning," a surprisingly profound meditation on what freedom means—both in politics and, perhaps more importantly, as a source of personal meaning.