Years before he became a fanboy icon while demanding kneeling by puny humans as General Zod in Superman II — and decades before he flaunted his versatility as an acerbic transsexual songbird in Priscilla, Queen of the Desert and an aging, raging badass in Steven Soderbergh’s The Limey — Terence Stamp was one of the dreamiest foot soldiers in the British Invasion of the 1960s.

During the era when it seemed that all the hippest music and movie stars were English imports, Stamp stood out — in films as diverse as Billy Budd, The Collector, Modesty Blaise and Far from the Madding Crowd — by memorably evincing a singular intensity that brought him almost as much attention as his rakishly handsome, if not downright beautiful, appearance.

Around roughly the same time, Vanessa Redgrave burst upon the international scene, earning her place of honor in a family of celebrated British acting talents. She, too, commanded rapt attention (and inspired more than a few impure fantasies) with variegated measures of beauty and vivacity.

She cast her well-nigh irresistible spell in such movies as Camelot, Isadora, Morgan: A Suitable Case for Treatment and, of course, Blow-Up — the latter being the film that spawned the classic poster of Redgrave with her arms strategically draped across her bare breasts, an image prominently displayed in multitudes of dorm rooms throughout the 1960s and beyond.

If you’re old enough to vividly recall the hubba-hubba heyday of these icons, consider this fair warning: Unfinished Song (at Magnolia Theatre) may be — during its opening scenes, at least — something of a brutal shock.

Stamp stars as Arthur, an irascible pensioner who behaves as though he views interaction with anyone other than his wife and drinking buddies as an annoyance he just barely endures (and even then, only if it can’t be avoided). Redgrave plays his wife, Marion, an appreciably more chipper golden-ager who takes pleasure in singing with a seniors choir in their small-town Northern England community, but whose joie de vivre is gradually diminishing because she’s terminally ill.

And, not to beat around the bush, both of them look awfully haggard. Which, as I say, is more than a little disconcerting.

I mean, geez, was it really that long ago that Redgrave shamelessly flirted with Tom Cruise in Mission: Impossible and he flirted back, and an erotic close encounter seemed a not-improbable possibility? And wasn’t it just the other day that Stamp kicked ass from one end of LA to another, and you had no trouble believing that almost everyone else on screen genuinely feared being next on his hit list, in The Limey?

But here’s the thing: While I don’t doubt that people who aren’t familiar with earlier films featuring Stamp and Redgrave may be entertained by Unfinished Song — indeed, I suspect that many ticket buyers who have never before seen either actor in any other movie could enjoy this one — it seems to me that longtime fans and admirers of both icons will be especially receptive to the charms of this intelligently sentimental and unexpectedly affecting dramedy written and directed by Paul Andrew Williams.

Why?

For openers, Williams does something very clever here by not telling us too much about the characters on screen. It’s not just that he doesn’t feel the need to explain each and every motive and relationship — like, we don’t know why James (a keenly subtle Christopher Eccleston), Arthur and Marion’s auto-mechanic son, is raising his 8-year-old daughter (Orla Hill) on his own. No, Williams goes so far as to tell us nothing about what, if anything, Arthur or Marion did for a living before they retired.

So, for all we know, they were actors with careers not unlike those of Terence Stamp and Vanessa Redgrave, and now they’re enjoying their twilight years together. That teasing possibility, as improbable as it might be, is more than enough to generate ample good will for the pair right from the start.

But wait. There’s more.

Unfinished Song (originally released in the UK as Song for Marion, an incontestably better title) is something far short of a cliche-free zone. Indeed, it skirts perilously close to caricature as some of the other folks in the seniors’ choir get their freak on while the peppy young volunteer choirmaster (Gemma Arterton) leads them through a song list that includes Salt ’n’ Pepa’s “Let’s Talk About Sex” and Motorhead’s “Ace of Spades.” (No, I’m not making that up.)

Here and elsewhere, Williams can’t quite resist the temptation to earn easy laughs with wacky geezers.

But when it comes to dealing specifically with Arthur and Marion, Williams is more respectful and resourceful. For one thing, Williams doesn’t write Arthur — and Stamp most assuredly doesn’t play him — as your standard-issue cranky golden-ager. For all his free-floating cantankerousness — and despite what evidently has been years of emotional estrangement from his son‚ Arthur is warmly attentive and affectionate with his wife when it counts and barely capable of disguising his mounting dread of being left alone in the not-so-distant future.

That Marion has little or no trouble dismissing Arthur’s surly disapproval and continuing as long as possible with the choir speaks volumes about the life they’ve lived together before we first meet them here. Obviously, she has never been a meekly dutifully wife routinely cowed by a crabby husband, and she’s not about to start now. So Unfinished Song is not just another movie about a long-suffering spouse who attains self-empowerment in her dotage. It’s actually something a bit more complicated — and a lot more satisfying.

When Marion takes a turn for the worse and must take to her bed, the choir shows up outside her home to serenade her with Stevie Wonder’s “You Are the Sunshine of My Life.” Marion is pleased and appreciative, but Arthur is angered, feeling that, once again, the choir is keeping his ailing wife from getting the rest she needs. So he gruffly demands that the singers disperse.

Marion demands that Arthur apologize. (And, mind you, she has ways of making sure her demands are met.)

Eventually, inevitably, he does apologize, albeit with all the enthusiasm of someone paying a parking ticket. And then he’s moved to do more.

You probably can guess what happens next, and what happens after that, and then after that. The pleasant surprises offered by Unfinished Song have little to do with its plot, which is unapologetically formulaic, and almost everything to do with the lead players and the roles they play.

Stamp and Redgrave are a match made in movie lovers’ heaven. And both stars are pretty damn close to incandescent as they portray vividly drawn, frail but feisty individuals who — each in a different way, but both with equal determination — rage against the dying of the light by lifting their voices in song.

Vanessa Redgrave and Terence Stamp star in Unfinished Song.

Courtesy photo

Vanessa Redgrave and Terence Stamp star in Unfinished Song.