London in the late 1940s, and all the clichés are true. It seems always cold and grey. Holes left by bombing still gape in the streets. Austerity and rationing remain in force. Life is a struggle, even for a self-confident young woman called Ruth Williams, with a promising job in the City.
It's hard in different ways for the handful of African students in London, even one so privileged and talented as Seretse Khama. Heir to the throne of the Bangwato people in British-ruled Bechuanaland, he's on his way to becoming the territory's first black barrister. For all the inconveniences of daily life, both young people have good reason to share a pervasive optimism. Their hardest choices can only be between good things. Will Ruth opt to remain a high-flying career woman, or for the conventional marriage and children she also wants? Will Seretse be a traditional ruler, or a modern professional man? Maybe one can have both...
When Ruth and Seretse met in 1947 it seemed to open another dimension of that future promise. They knew life together wouldn't be easy. It would be hard to win her parents' approval. Seretse faced difficulties persuading his uncle, the Bangwato's chief.
Yet their planned marriage surely meshed perfectly with the best hopes of a new, more egalitarian Britain, and an Africa headed fast for self-government. Their backgrounds and characters seemed designed to confound the prejudices of racists in Britain and of Puritan Bangwato elders: apparently, they didn't even sleep together before marriage. Over 30 years later, I asked Lord Hailsham, one of the few Tories to back them, why he had done so. I recall his words exactly: "She was a very respectable girl. Very decent family. If she'd been some cheap little trollop..."
It all turned into a long nightmare for the couple. Such a liaison was unacceptable to the white settlers of southern Africa, and to South Africa's government. Official Britain felt it needed to appease both. So ministers and civil servants tried for years to prevent and then destroy the marriage, using every dirty trick. The sheer dishonesty and nastiness chronicled in Susan Williams's wonderful account still startle. Snobbery and sexism were only a little less rampant than racism.
At the end, Ruth and Seretse's love triumphed, with the help of a brave anti-racist minority in Britain and the overwhelming solidarity of the Bangwato people. In many such late-colonial morality plays there is a depressing second act, where heroes and heroines turn into oppressors or crooks. For the Khamas, and Botswana, this is not so. There is sadness that Seretse lived only to 59, but the wider story remains upbeat.
Ruth remained beloved by and devoted to her adopted people. Botswana has prospered, with high rates of economic growth and one of Africa's few genuine democracies. Alexander McCall Smith's Botswanan detective stories are the latest indication that Botswanans are Britain's favourite Africans. Even if such an image serves only to offset the fear many feel for the rest of the continent, the Tswana have earned it. Williams's book is a tribute not only to a remarkable couple, but to a people whose grace under pressure is hard to match anywhere in the world.
Stephen Howe is a professor of history at Bristol University