Some members of the Kikuyu tribe emigrate to a terraformed world to create an utopia that resembles how they lived before the Europeans with their corrupting influence came.
The subtitle of the book is A Fable of Utopia, which is ironic, since the main character is the witch doctor of his people who tells them fables that always have a hidden lesson. The lesson of the book Kirinyaga is about the unattainability of utopias, because life is change and utopias are not, and if they are realized at all they exist only for a small, fleeting moment in time until change sets in. Which is not a particularly new lesson, but one that bears repeating and retelling, and like the fables that Koriba the witch doctor tells, the best way to do this is to hide the lesson in something entertaining. And Kirinyaga has some of the most touching stories that first and foremost convince as stories, even if they have some lesson inside them.