The opening title "Based on a true story" can cover a multitude of movie sins, but in "A United Kingdom," it unlocks the door to a romantic drama that grows more remarkable by the minute.
While lovers faced with daunting obstacles is a dramatic tradition going back to Romeo and Juliet, if not further, the real-life barriers facing Seretse Khama (David Oyelowo) and Ruth Williams (Rosamund Pike) when they fell in love in 1947 London were unusually intimidating and overwhelming.
The African Khama and British Williams had to contend with more than casual British racial prejudice, more than the taunts of yobs on the street or even the horror of Williams' own father, who tells his daughter, "You disgust me." Much more.
For Khama was not simply a handsome and charismatic African, he was also a prince of his native country, the British protectorate of Bechuanaland (now Botswana), and about to become king. And Williams was on the surface simply an ordinary office worker, leading to taunts like "a chief cannot pluck a girl out of the typing pool."
Back home, not only were Khama's sister and the aunt who raised him aghast at the match but so were big chunks of the country's population, especially his regent uncle Tshekedi Khama (an effective Vusi Kunene), who felt he was compromising Bechuanaland's future and demanded he abdicate the throne.
More than that, the love match between these two caused serious international political dislocations. Bechuanaland's neighbor South Africa, starting to implement its racial separation policy of apartheid, was furious at what it considered an affront, and as an influential member of the Commonwealth, that country had enormous sway with British policy toward the protectorate.
Quite a lot for a young couple to contend with; as written by Guy Hibbert ("Eye in the Sky," "Omagh") and directed by Amma Asante ("Belle"), "A United Kingdom" does a satisfying job of keeping all these balls in the air.
"A United Kingdom" is traditional, well-made cinema, with a taste for the obvious at certain points, but it has some powerful advantages. These include its remarkable story (Susan Williams'' book "Colour Bar" was a primary source), plus a director who knows how to convey its essence and a superior cast whose presence elevates the material.
Costar Oyelowo, persuasively sensitive as well as strong, has been connected to the project since even before his role as the Rev. Martin Luther King Jr. in 2014's "Selma" brought him to prominence.
The actor helped persuade Pike, much sought after after playing the disappearing Amy in "Gone Girl," to take the role of the unwavering Williams.
And he wanted Asante after seeing "Belle" because he felt, the press notes relate, "she convinces the audience that two people are falling in love before their eyes."
Along with its willingness to honor the story's complexity, it is that ability to make us believe that these two people have become so truly and deeply in love that they can withstand whatever the world throws against them that keeps "A United Kingdom" involving.
Certainly falling in love was hardly on Williams' mind when she accompanied her sister Muriel ("Downton Abbey's" Laura Carmichael) to an earnest event called the Missionary Society Dance.
There she meets Khama, and the two bond over a mutual love of American jazz, and, as it turns out, the energetic swing dancing they convincingly take part in as their attachment deepens.
The reveal to Williams that Khama is no ordinary African but a future leader comes fairly early on, and "A United Kingdom" is especially good at conveying the attraction that continues to bind them even though they know it doesn't make sense. "I will never achieve anything," he tells her, "if I leave my heart here."
Inevitably less convincingly portrayed are the string of myopic Foreign Office Brits like Alistair Canning (Jack Davenport) who have their devious, distinctly nonromantic reasons for trying to derail this love match. When Canning threatens Khama with the assertive "now you will see how an empire defends itself," he is for once being completely candid.
By contrast, the film's portrayal of key Africans, starting with but not limited to Oyelowo and Kunene's performances, is one of "A United Kingdom's" strengths.
The film's most effective nonromantic scene, in fact, has Khama's sister Naledi (Terry Pheto, from the Oscar-winning "Tsotsi") and his aunt Ella (Abena Ayivor) having a "why would you do this to us?" confrontation with Williams that has both substance and bite.
Though it engages in some not surprising simplifying of complex events, "A United Kingdom" also displays a welcome yearning for fidelity, with cinematographer Sam McCurdy shooting exteriors in Botswana, including Khama and Williams' original home in the village of Serowe (which the film crew sought out and refurbished).
The married couple's real-life battles against the forces arrayed against them were fought one skirmish at a time over a number of years. "A United Kingdom" understands that it was by no means easy, but emphasizes the centrality of their determination not to allow "the world's ugliness to take our joy away." They don't, and we are all the better for it.
"A United Kingdom"
Rating: PG-13 for some language, including racial epithets and a scene of sensuality
Running time: 1 hour, 51 minutes
Playing: ArcLight, Hollywood; Landmark, West Los Angeles