In Book 1, we follow Reverend Stephen Kumalo's quest to find his lost brother, sister, and son.
The first—and longest—part of Cry, the Beloved Country deals with country priest Stephen Kumalo's confrontation with the Big Bad City, Johannesburg. The temptations of Johannesburg (alcohol, sex, money, and power) lead Kumalo's lost family members in some pretty dark directions. His sister Gertrude becomes a prostitute and a seller of illegal moonshine. His brother John becomes a puffed up, greedy politician. And worst of all, his son Absalom becomes a robber and a killer.
But Paton tries to present these crimes in a sympathetic light, by emphasizing that they are the result of a lack of opportunity and cultural support among black South Africans now that traditional tribal morality has been destroyed by white colonialism. What has happened to Kumalo's family is a symptom of a sickness in South Africa as a whole.
In Book 2, now that Kumalo has found his family members, we have to discover what exactly he is going to do with them.
The thing is, Kumalo's original plan is to bring everybody back together in Ndotsheni: Absalom, Gertrude, and John. Now, John is firmly attached to Johannesburg's political scene (and he likes the power too much to want to go back to his little village). Gertrude has said that she wants to live the quiet life in Ndotsheni, but she's obviously too used to partying in the city to head home with her much older, stuffier brother. And Absalom is condemned to death for the killing of Arthur Jarvis.
So Kumalo's plans have all come to nothing. Now, all that remains is for Kumalo to find some source of new hope to rebuild his life in Ndotsheni.
Book 3 of the novel brings together James Jarvis (the father of Absalom's shooting victim) and Kumalo to reform Ndotsheni. Back in his home village, Kumalo tries to reform the education system so that people will have new opportunities for work in the countryside and they won't feel the need to leave for Johannesburg. Having lost his family to the city, he wants to create new chances at home so that the next generation—his grandson and his young nephew—won't face the same struggles that Absalom and Gertrude faced. However, Kumalo doesn't have enough influence on his own to get anything done.
Thankfully, James Jarvis has responded to his son's death with sympathy for Arthur's desire to reform South Africa's racist social institutions. So Jarvis helps Kumalo improve Ndotsheni's agriculture, provide milk for the village children, and renovate the crumbling old church. With Jarvis's financial backing, Kumalo really starts to see hope for the future of Ndotsheni, even if, as an old man, he may not live long enough to see real change come to South Africa.