What is the theme in Mrs. Plum by Ezekiel Mphahlele?

One important theme in the novel is civil rights.

Although they are the vast majority of the population of South Africa, the black Africans in the story do not share the personal rights that members of the white minority enjoy. The blacks are required to carry an identification document called a "pass" at all times, and they can work and travel only in the areas specified on the pass. Dick does his best to please his employers, because he knows that they could sign his pass at any time and force him to leave the district. When the police come to search for black servants who do not have the proper passes, they do not need a warrant or any reasonable cause to search Dick's and Karabo's rooms, and the servants have no right to refuse the search.

When Karabo is at the Black Crow Club, she listens to lectures by Lilian Ngoyi, who points out the injustices of South African minority rule. Ngoyi urges her followers to work toward a day when the government represents all the races and classes of South Africa, and when all South Africans are citizens with equal rights. Karabo finds Ngoyi's dreams of a united and equal South Africa intriguing. But because blacks do not even have the right to vote during the time of the story, the idea of them sharing political power seems impossible.