The film unfolds the incredible true story of Seretse Khama, the heir to the throne of Bechuanaland, who pursued his law studies in London immediately after World War II. During his time there, he encounters the Englishwoman, Ruth Williams, whom he marries in 1948 despite facing significant opposition from their families and the British government. The authorities were deeply concerned about the implications of their union on relations with South Africa and the stability of the southern Africa region.
The National Party government in South Africa harbors a fear that a marriage between a black king and a white woman in nearby Bechuanaland would incite upheaval, particularly since they were attempting to outlaw such unions. To curb the marriage, they pressure the British government, alongside the administrations of South West Africa and Rhodesia, to intervene.
Additionally, Khama's uncle, the Regent, implores him to abandon his marriage and instead take a Bamangwato princess as his wife, a request that Khama defiantly rejects. The British officials leverage this conflict to claim that the marriage is a source of unrest. In the midst of this turmoil, Seretse discovers that British officials have permitted a US mining corporation to explore for valuable minerals and is determined to ensure that the resources of Bechuanaland are managed by its own people if anything is found.
In a bid for public support, Khama manages to rally his community, leading the British to decide on his exile. While this takes place, Ruth gives birth to their child and gradually earns the respect of the local populace by “walking the road with them.” As tensions rise, the British is determined to replace the king with an administrator, but the tribe's refusal to call the necessary meeting halts their plans.
In a pivotal moment, British Prime Minister Clement Attlee confides to backbencher Tony Benn that the nation requires South Africa's gold, implying that dismantling the Khamas' marriage is a compromise worth making. In a twist of fate, diamonds are discovered in Bechuanaland, and Khama ensures that the British government recognizes the sovereignty of the Bechuanaland people over these newfound resources.
While Winston Churchill promises to reinstate Khama's leadership upon his election, he instead enforces an indefinite exile. Yet, Khama garners support from influential figures in London and the US. Meanwhile, the rise of apartheid in South Africa casts a deep shadow over Bechuanaland.
Ultimately, through the advocacy of local communities, Khama is permitted to return and leads the charge for independence from British rule. He confronts his uncle with a revealing British government document that validates his qualifications as a king, exposing the British hostility as a mere reflection of South African opposition.
In an uplifting conclusion, the film reveals that Khama would become the inaugural president of contemporary Botswana, and that their son would later serve as the country's fourth elected president in 2008. The poignant narrative wraps with the touching image of Ruth and Khama together in eternal rest on a hilltop overlooking Serowe village, where they lived out the rest of their days.
