Remember the love story of Aragorn and Arwen — the Man Who Would Be King and the Eyebrow-Pencil Elf, both of them signing on for civil unrest and personal heartache by pledging themselves to one another? Remember how this infuriated her father, who did what he could to keep them apart?

We know how that turned out. After tears and trouble and promises and heartbreak, the result was… a united kingdom!

That just happens to be the title of a new and not-so-fictional 1940s drama. A United Kingdom is about another pair of lovers so passionately smitten that the production might have been better conceived as an opera.

Amma Assante, director of Bella, must have jumped at the chance to tell this epic story, one so fraught with “You’ve Got To Be Kidding Me” twists and turns that it’s a wonder it hasn’t already turned into a multi-episode Masterpiece Theater event starring Idris Elba and Sienna Miller. Perhaps it’s for the best. A United Kingdom arrives in a timely fashion, as conscientious moviegoers have an urgent need to see some inspiring stories of victories over racism — especially some examples of undeniably joyous and appealing interracial marriage.

Rosamund Pike and David Oyelowo in A United Kingdom, from BBC Films.

But I can’t help thinking that this movie could have brought together the Man Who Would Be King of Botswana and his beautiful English clerk more persuasively if it has been given the running time of a mini-series. Alas, screenwriter Guy Hibbert tells the tale with an annoyingly unimaginative matter-of-factness, as if someone’s set a two-hour timer for him to complete his storytelling.

I wouldn’t be surprised to learn that Assante wanted three hours to unpack such lengthy, complicated story, but the studio gave her only two. I have no evidence that this was the case, save for the narrative’s breathless pace — you can feel the editors watching rough cuts and lamenting that each sequence needs to be 30 seconds shorter. I can’t remember any sequence playing long enough that it felt like, well… a scene. And I lost track of how many moments began to show promise, but then leapt forward in time and space so fast that my film-reviewer’s note pad was useless, busy with incomplete sentences. At times, it feels like one of those high-speed, community-theater versions of Shakespeare, with the actors dashing about and changing costumes even as they deliver their lines.

The result is a movie so impatient with politics, and so (disappointingly) uncurious about the culture that King “Don’t Tell Me Who I Can Love” and Queen “Throw Caution to the Wind” will have to rule, that if its central love story didn’t work, there would be very little worthy of our attention at all.

Fortunately for moviegoers, Assante’s two leads are so adorable and charismatic together that it’s easy to root for them.

It’s a case of perfect casting.

David Oyelowo, who was Selma‘s charismatic Martin Luther King Jr., plays Seretse Khama, bringing similarly dutiful nobility to this role, but with a little more humor and tenderness. He’d better change things up quickly, though. He’s in danger of being typecast.

We’re blessed by the always-radiant Rosamund Pike in the role of Ruth Williams. Pike tends to shine brighter than anybody else in whatever movie casts her (including Gone Girl, An Education, and, I would argue, Joe Wright’s Pride and Prejudice), and that’s the case here as well.

These two give us the kind of love-story model that parents could easily watch with their kids without blushing. That’s a fact that, I admit, I found a bit disappointing. One gets the feeling there might be even more, um, enthusiastic footage left out. Pike in particular throws herself into this as if Oyelowo is the actor she’s always wanted to love onscreen.

The film’s surprisingly high Rotten Tomatoes score may reflect the fact that the soon-to-be-royal couple are charming enough to make tomato targets out of anybody who stands in their way — which, in this case, seems to be the whole wide world. And that includes her father, her neighborhood, her government, his uncle, his sisters, and his people.

Is that one of the devil’s horns from Ridley Scott’s Legend behind Jack Davenport here?

As the most despicable obstacle of all, Sir Alistair Canning (the name itself screams “Pain in the Crumpet!”), we get the unfortunately named Jack Davenport. Davenport’s familiarity to fans of Pirates of the Caribbean may incline them to suspect that he’s actually trying to steal this African’s king’s bride for himself. (He’s not; Sir Canning is already married to a woman who looks like a villain from Sherlock.)

Canning seems to be waiting around every corner, eager to deliver more bad news that will spoil the lovers’ wedding, honeymoon, marriage, and eventual parenthood. He’s so convincingly nasty, I wondered if maybe he’s venting some deep resentment at the world-conquering success of his younger model — Benedict Cumberbatch. I half-expected his face to spontaneously generate a standard-issue Villain’s Mustache just so he could twiddle it. (Leave the mustache twiddling to Rufus Lancaster, the district commissioner, played by Tom “Draco Malfoy” Felton, still the big screen’s most punchable face.)

To peeves in a pod: Jack Davenport and Tom Felton as villains in A United Kingdom.

You’ll notice that I’m not divulging the complicated details of this historical, intercultural scandal — and that is, in part, because the movie digs about as deep into those complexities as a high school history paper. If I explain it all here, there won’t be much left to surprise you.

Suffice it to say that Seretse is in England to study and prepare for his eventual inheritance of Bechuanaland’s throne. Of course, all we see of him there are his moves in the boxing ring (he’s a fighter, you see!); his magical love-at-1st, -2nd, and -3rd-sight entanglement with Ruth; an abrupt proposal; and the inevitable shows of unenlightened distress from family and community (including, of course, Seretse defending his honor against racist bullies as he walks Ruth home from a date).

Though Seretse wants to bring Ruth back to Africa, he warns her of troubles ahead. She’s blinded — or at least a little deluded — by love, and signs on for the marriage anyway. Surely, in the real world, these two brought more intellectual rigor to their commitment. Here, they just seem sweet and naive. I confess that I, at times, feel some sympathy for the exasperated officials who seek to keep them apart, thinking, “Seriously, how many lives are at stake here? Are they really so blind to the potential consequences of this engagement? This sort of thing could spark a war!”

Whatever the case, Ruth soon finds herself a stranger in a strange land, the recipient of relentlessly critical scowls. Bechuanaland is a British protectorate alongside South Africa, you see, where the rising specter of apartheid threatens to make the natives’ lives miserable, and the pending discovery of “mineral assets” jeopardizes any claim that the people have on their home and their future. Why would they want a white queen?

Well, it must have been a devastating drama to watch unfold in the news of the day. And I can’t imagine what it took for Ruth and Seretse to endure what they did. But here, the farther the movie draws us into the drama, the more we lose our grip on the lovers who enchanted us in the opening act, until the movie becomes an inevitable countdown to the moment when the strategy in casting Oyelowo becomes clear, and he gets to make his Oscar-highlight speech — a rallying cry worthy of Aragorn himself. But it feels like too little, too late.

Leaving the theater, I found myself trying to recall a single memorable image in the film’s full running time. Oh, there’s pleasure in seeing two excellent actors find chemistry like this. But the movie’s most significant effect is in how it makes us marvel that this story ever took place, that it could really be true. That, in itself, is a hope-inspiring thing. And perhaps, in this deeply troubling season, as the world’s hopes for peaceful multiculturalism seem dangerously close to collapse, that is enough.