It’s hard to believe that Mahershala Ali has never been the lead role in a film before, but Benjamin Cleary’s elegiac “Swan Song” is eager to make up for lost time: Not only does Ali get to play the protagonist in this somberly moving sci-fi drama about a dying man who secretly clones himself in order to spare his family the heartache of living without him, he gets to play him twice. The original Cameron Turner is a sad-eyed illustrator whose inner warmth is only drawn out through the tip of his pencil. In fairness, this movie’s sleek and corner-less vision of the near-future seems like it would make introverts of us all, as Cleary’s debut imagines the day after tomorrow as a place so dominated by wearable tech — specifically membrane-like airpods and contact lens operating systems with UIs that make this Apple Original look as if it’s been adapted from Jony Ive’s wet dreams — that everyone is walled inside their own invisible bubbles, even when they’re sitting across from each other on the same train.

The playful meet-cute between Cameron and his one-day wife Poppy (Ali’s “Moonlight” co-star Naomie Harris) hammers that point home in a hurry, as the two commuters nibble away at the same chocolate bar as if they’ve known each other all their lives. He chuckles at her with each bite, convinced that this beautiful stranger is eating the snack he just bought, only to realize later that his chocolate bar is still in his pocket, and that he was the one acting weird. The scene makes for a slyly brilliant introduction to a fable that will soon be wracked by more philosophical questions of what belongs to whom, and how best to savor the sweetness of our lives in a world where everything can be shared — including our lives, themselves. If Cleary’s prologue evokes memories of the meet-cute from “Eternal Sunshine of the Spotless Mind” in the process, that also proves to accurately foreshadow a movie that uses a fanciful procedure as scaffolding for a story about someone trying to pave over their deepest pain. Then again, that’s also the last of their commonalities; where Michel Gondry’s film was kooky and percussive, this one is as morose as a rainy March afternoon, with Jay Wadley’s mournful string and piano score achieving such urgent dystopian sadness that at one point it seamlessly blurs into the Wooden Elephant version of Radiohead’s “Idioteque.” The details of that sadness reveal themselves soon after “Swan Song” skips forward to its unsettled present (a relative term in a film pockmarked with flashbacks that strive to convey the sense of a person remembering their life for the last time). Cameron is dying of a terminal illness of some kind, an illness that he’s hid from the now-pregnant Poppy and their young son Cory because their family has finally started pulling itself back together after the sudden death of Poppy’s twin brother and the marital drift that followed. “We haven’t been us in a while,” Poppy says, as if inadvertently permitting her husband to swap himself out for a different model. It seems like only a matter of time before Cameron has to share the bad news with his loved ones, unless… unless Dr. Scott can suggest a better idea (Glenn Close reprises the mad scientist mode she owned so well in “The Girl with All the Gifts,” another movie about a white lady playing God with reluctant patients of color).

 Operating from a remote Vancouver facility so edgeless and sterile that it feels like she’s just Airbnb-ed Denis Villeneuve’s summer house, Dr. Scott is ready to make Cameron the same offer that neither of her prior two patients were able to refuse: She will create a perfect clone of Cameron minus his illness, endow him with all of Cameron Prime’s memories (not including the duplication procedure), and send him back to “his” family so that everyone can live happily ever after. Everyone, that is, save for Cameron himself, who will have to spend his few remaining days cooped up in Dr. Scott’s lab, with only her previous subject for company (she’s played by Awkwafina with a degree of “it is what it is” fatalism that brings a few light smiles to a movie that’s otherwise about as funny as a pregnant widow). The wheels are in motion well before Cameron ever arrives at Arra Labs, and there’s no doubt that his duplicate will come online at some point. That doesn’t prevent “Swan Song” from expressing (too) much of its drama through the material process of bringing that clone to life, but the film is still less interested in the suspense of it all than it is in the more abstract questions that are inevitably raised along the way. Is it ethical to keep Poppy and Cory in the dark? Is it possible to export a man’s essence, and if so, what is it that makes us who we are? Most of all: How could someone in Cameron’s position make peace with the idea that life — specifically their life — continues without them? Like most of the speculative sci-fi movies that hinge on such existential dilemmas (the more intense “Ex Machina” comes to mind), “Swan Song” is frequently held hostage by its own concept. This is a film as smooth as its minimalist architecture and cozy self-driving cars — one in which the premise itself is the main attraction, and the human characters are just passengers in the traffic that flows around it — but Ali’s dual performance is so inextricable from what Cleary is doing here that Cameron is able to retain a measure of personal agency. While the parts when Ali wrestles with the “should I or shouldn’t I?” of it all leave precious little room for individualistic detail, the scenes in which Cameron squares off with his clone are electrifying for their instability. A simple dress code helps us tell the Camerons apart, freeing Ali to focus on their similarities and shine a beam on the tiniest photons of light that define the difference between them. The nuances of his performance(s) reverberate with the uncanniness of hearing your own voice echo back on the other end of a phone call, leaving us to wonder at why these two men aren’t just saying the same things in perfect unison, or if they’re actually two men at all.

Is it the circumstance that separates them? Have they been wandering down separate paths from the moment they began having separate experiences? The film’s most arresting insides unfold like a kind of solipsistic group therapy. At first it seems rather feckless to build this movie around a fundamentally decent guy whose recent depression won’t ever prevent him from doing the right thing, but as the Camerons begin to hash things out, that moral compass starts to point in compelling new directions. That being said, “Swan Song” resonates more for where it winds up than how it gets there, with Cleary’s script reducing Poppy to a “sad wife” stand-in whose only defining characteristic is that she kind of speaks French, and eventually indulging in a predictable detour towards thriller territory (albeit with an underplayed sense of grace). Throughout the movie, his didactic approach to the camera — locked off and numbing in the moment, handheld and chaotic in Cameron’s memories — doesn’t serve the story’s undercurrent of duality so much as it mutes the emotion of the movie’s biggest decisions. Still, I was moved by the honesty with which “Swan Song” is able to crystallize all of its airy ponderousness and sci-fi protocol into the kind of teary-eyed clarity that hits us where it hurts in the here and now. At its core, this is an iPod-shiny parable about the pain of being left behind, and one that — like so much of the best sci-fi — poignantly literalizes some of the the anxieties that have dogged humanity since the dawn of time. It might look a bit different tomorrow than it does today, but even a lifetime spent in Dr. Scott’s James Turrell-esque memory palaces wouldn’t change the simple fact that being left behind is what we’re born to do. At a certain point it just isn’t about us anymore, even if the people we love might swear that we’re still there.

Grade: B

“Swan Song” premiered at AFI Fest 2021. It will be released in theaters and available to stream on AppleTV+ on Friday, December 17. Sign Up: Stay on top of the latest breaking film and TV news! Sign up for our Email Newsletters here.