“Swan Song,” a reunion project for “Moonlight” alumni Mahersala Ali and Naomie Harris, is quiet, introspective science fiction about a dying man’s struggle with the notion of cloning himself and letting that clone take over his life shortly before his death.

“Introspective” is becoming something like the two-time Oscar winning Ali’s brand, as he often plays brooding, thoughtful and soft-spoken characters capable of the occasional burst of fury (“Green Book”).

But writer-director Benjamin Cleary’s debut feature does neither Ali nor himself any favors. The movie’s so low-key and low-heat that it’s slow. And with that lack of pace we’re forced to confront, often, how over-familiar this story, this version of “the future” and this film are.

Start with the idea of second-guessing a second chance at life via cloning.” It wasn’t the freshest notion when “Seconds” crossed that threshold in the 1960s. There’ve been whole TV series about cloning and other films in which characters wrestle with the ethics of extending life — often their own — this way.

The very first scene of the movie is borrowed from another movie as well. It’s a “meet cute,” with graphic artist/designer Cameron (Ali) ordering a chocolate bar (from a robot) on a commuter train of the near future.

A bubbly, distracted stranger (Harris) sits down, chattering away on her phone. She distractedly opens the candy bar and starts eating.

Cameron is a little surprised, and intrigued enough to be bold and do the over-familiar thing. He breaks off a piece of the bar as well. This goes on, with a few exchanges of coy, flirtatious looks. We can’t tell if she’s put-out or pleased, as he seems to be.

He generously gives her the rest of the bar as she leaves. She smiles. And when his stop arrives, he stands up and discovers…the candy bar he bought earlier. The whole shared-food thing was a mistake, and he laughs and laughs.

So do we. Even if we remember the classic short film that invented that bit. Don’t tell me Cleary, who won an Oscar for a short he made a few years back, hasn’t seen 1989’s “The Lunch Date,” one of the cinema’s greatest short films, now preserved in the National Film Registry.

“Swan Song” picks up its story some time later, as Cameron keeps a big secret from the “lunch date” Poppy who is now his wife and the mother of their little boy. He is having seizures. He has cancer. He’s dying.

And there’s a second big secret. There’s a new firm offering him an option. He’s off for a weekend to seal the deal, one of the first-ever customers of Arra House, run by Dr. Scott (Glenn Close) and her trusted assistant (Adam Beach). They, and their vast AI tech lab offer “molecular regeneration,” a replacement Cameron, “right down to the molecule.” His clone is his actual twin, and meeting it unnerves him. He flees.

But there’s still time. Dr. Scott is persistent. And Cameron is still keeping all this secret from Poppy. Once she sees him sick, or heaven forbid, he dies in front of her and their child, the “option” Arra
House affords him will be gone.

“Swan Song” is about his internal debate over the ethics, morality and surrender that doing this will entail. Cameron will be surrendering his life, before death, so that his family can go on as if nothing happened. Can he do it? Would you?

Cleary gives us routine “this is what the future will look like” peeks. The future tech includes cameras in our contact lenses, holographic displays everywhere — in 3D monster boxing match games Cameron plays with his child.

Sleek, self-driving taxis, austere, curved, minimalist architecture, a world that isn’t overpopulated, over-polluted, over-heated and fascistic –you’d have thought this naive, idealized future would be something the cinema had grown out of. We can’t even ban machine guns for teenagers in this country. How in hell are we going to solve even bigger problems?

There are pop-up partitions Dr. Scott can switch on from her phone to give Cameron privacy as he “tests” this clone in phone interaction with his wife. Which he does. He meets another “client” of Harrah House, a funny downtown realtor (the ever-adorable Awkwafina), also dying, but perhaps more accepting of this transition.

As he checks the “memories” transplanted to his clone, Cameron remembers the life he is losing, the troubled stretches in the marriage, the “future” he won’t be around to see.

Ali’s showiest scenes are when he debates his “molecular regenerated” self, the flashes of temper he drops on the doctor and the clone’s troubling adjustment to “his” home.

But even those heated moments lack much of a punch. There’s not much meat to the performances, which is understandable as “Swan Song” is redigesting subject matter that’s been covered before, and often. It’s as if the cast and director figure we’ve seen straight-forward treatments of this subject. Now is the time for an understated, impressionistic riff on cloning ethics and human choices — too understated.

The light moments are so rare and the emotional outbursts likewise that the autumnal (overcast) lighting, somber music and quiet conversations of “Swan Song” are in danger of putting the viewer to sleep.

Not a ringing endorsement, but it’s hard to think of this as anything but the first misstep in Ali’s formidable post-Oscar career.

Rating: language (profanity)

Cast: Mahersala Ali, Naomie Harris, Glenn Close, Adam Beach and Awkwafina

Credits: Scripted and directed by Benjamin Cleary. An Apple TV+ release.

Running time: 1:52