1947. Seretse Khama (David Oyelowo) the King of Botswana, met Ruth Williams (Rosamund Pike), a London Office worker. The attraction was immediate; she was captivated by his vision for a better world, he was struck by her willingness to embrace it.

They were a perfect match, yet their proposed marriage was challenged not only by their families but by the British Empire, amidst the background of apartheid in Botswana's neighbour, South Africa, who lid down an ultimatum--either deny Seretse and Ruth's marriage, or be denied access to South African gold and uranium. Despite the terrible pressures they faced, Seretse and Ruth never wavered--they fought for their love against incredible odds, against an Empire they united a Kingdom.