A hero falls under the shadow of the dark power.
Christopher Booker's "dark power" makes it sound like Cry, the Beloved Country is actually Lord of the Rings, but sadly, there is no Sauron involved in Paton's plot. In this case, the "dark power" that overwhelms Kumalo at the start of the plot could be one of two things: (1) specifically, Kumalo's loss of contact with his brother, sister, and son; or (2) more generally, the high rates of poverty and unemployment within the black community in South Africa, which drives many of Kumalo's family members away from their home village. In either case, Kumalo decides to travel to Johannesburg to try and save his family from destruction.
For a while, all may seem to go reasonably well.
In fact, with Msimangu's help, Kumalo finds his sister and brother relatively easily. That "dark power" appears to be lifting from his life after all. Yes, Gertrude is living a rough life as a prostitute and John seems to have grown distant and greedy over the years away from home. But at least Kumalo has seen them again, and Gertrude even agrees to return with him to Ndotsheni with her son. Kumalo starts to feel more upbeat about the possibility of rebuilding his family, particularly as he feels himself getting closer and closer to finding his son.
But eventually, it approaches again in full force, until the hero is seen imprisoned in the state of living death.
Kumalo may feel upbeat for a time after Gertrude packs up her belongings and joins him at his boarding house. But of course, that period of hopefulness doesn't last long. Kumalo finds out that his son has been charged with murder. And even if Absalom didn't intend to shoot Arthur Jarvis, he still broke into the man's house carrying a gun, which horrifies Kumalo. Absalom is condemned to death for Arthur's murder, and Gertrude disappears just before Kumalo travels back to Ndotsheni. So all of Kumalo's dreams of having his family around him in Ndotsheni once again appear to be ruined.
This continues for a long time. When it seems that the dark power has completely triumphed …
Kumalo returns home to Ndotsheni with Gertrude's young son and Absalom's now-wife. His son is going to be executed for murder, which is grim. And Ndotsheni continues to struggle, without enough milk for the kids and without enough rain for the crops, which is also grim. Kumalo tries to arrange for new agricultural education in the village school to help improve the local farms and encourage kids to stay on in the village, instead of heading to Johannesburg for work. He wants to make sure that future generations have opportunities in Ndotsheni that Absalom didn't have. But he is an elderly priest, and he doesn't have a lot of political authority to get things like that done.
But finally comes the miraculous redemption.
But then, James Jarvis comes to the rescue. Jarvis lives on a rich farm near Ndotsheni, so he is familiar with the village. And instead of responding to his son's shooting with hatred, Jarvis has been reading all of his son's papers on improving the social conditions for black people in South Africa.
Under his son's influence (and with some unexpected hints from his young grandson), Jarvis sends milk to Ndotsheni for the children. He arranges for a new farming instructor for the village. And he donates money to Kumalo to rebuild the village church. With Jarvis's money to help him with his plans, Kumalo finally sees some hope for the village of Ndotsheni as a whole, even as he awaits the execution of his only son.