Part I - "The Waning Light"
Weep Not, Child is set in a Gikuyu village in Kenya during the 1952-1960 Emergency, a tumultuous and violent period which would eventually lead to Kenya's independence from Britain.
One day, the beautiful Nyokabi offers her youngest son, Njoroge, an opportunity to go to school. He enthusiastically accepts, even though he knows it will be a financial stretch for the family. His prospects are contrasted with those of his half-brother Kamau. Although Kamau is only slightly older than Njoroge, he has already been apprenticed to a carpenter, and will pursue that instead of going to school. Both boys hope that their training will lead them to a happy and successful future.
The village is located near Kipanga, a larger town where many of the villagers work. Kipanga is home to many colorful characters, including a funny barber who tells colorful stories about his experiences fighting in World War II. On this day, Njoroge and Kamau’s father, Ngotho, is spending time in Kipanga. He soon returns home, proud that his son will be the first in the family to attend school. Ngotho works as a farmer for a British land-owner, Mr. Howlands, on land that Ngotho's family once owned.
Njoroge initially has a hard time adjusting to life at school, but his old friend Mwihaki helps him. Mwihaki is the daughter of Jacobo, a rich Gikuyu pyrethrum farmer who owns the land that Ngotho and his family live on. One evening, Ngotho tells his wives and children – Kori, Boro, Kamau, and Njoroge – stories about how the British stole the Gikuyu land. These events particularly upset Boro, who believes his father complicit in the injustice by working for Mr. Howlands. Boro has been troubled ever since he lost his brother when they were fighting together in World War II.
Njoroge enjoys learning how to read - and eventually, how to speak English. He continues to bond with Mwihaki, and also dedicates himself to studying the Bible. He sees parallels between the Gikuyu struggle and the oppression of the Israelites. Meanwhile, Kamau is frustrated by the slow pace at which his boss, Nganga, teaches him.
Word spreads through the community about a strike to advocate for more rights for Africans. Ngotho wants to participate, but is worried that Mr. Howlands will fire him. He decides to walk out anyway, and attends a rally where Boro and his friend Kiarie are scheduled to speak. The police bring in Jacobo, who urges the strikers to return to work. Ngotho is so enraged by Jacobo that he rushes the stage and attacks him, which starts a riot. The riot is put down immediately, and has dire consequences for Ngotho’s family – he is fired from his job and evicted from Jacobo’s land. Fortunately, Nganga allows the family to move onto his land.
Two and a half years pass. Njoroge’s hero, the revolutionary Jomo Kenyatta, is arrested. Meanwhile, there are many incidents of violence by the Mau Mau, one of the revolutionary groups. The whole culture is in a state of flux and worry.
Part II - "Darkness Falls"
Njoroge’s older brothers Kori and Boro both have run-ins with the police. An atmosphere of fear permeates the village; people are afraid not just of the police, but also of the Mau Mau, which slits the throats of suspected traitors.
Mr. Howlands and Jacobo plot ways to arrest Ngotho, whom they both resent for his insubordination and his attack on Jacobo. They arrange for Kori and Njeri (Ngotho’s first wife) to be arrested, although Mr. Howlands is reluctant to harm Ngotho because he remembers how much his old employee loved the land. Meanwhile, Njoroge’s school is threatened by the Mau Mau, but he continues to attend at Kamau's advice.
One day, Mwihaki returns to the villages after several years away at boarding school. She and Njoroge are happy to see each other, and she invites him into her home, where he is surprised that Jacobo is so kind to him. They promise to be together after she graduates. Not much later, Njoroge and some friends go on a church retreat. However, the retreat is stopped by the police, who murder their group leader for his attitude of independence. Meanwhile, Boro plots ways to murder Jacobo.
Njoroge is promoted to high school, and Mwihaki, whose grades are not as strong, attends a teaching college. The differences between them become more apparent – Mwihaki is frustrated and hopeless about the state of the country, whereas Njoroge believes that educated young people have the power to change the future. At high school, Njoroge flourishes. One day, he meets Stephen Howlands, the son of Mr. Howlands. The two boys realize that they have much in common, and discuss the reasons that they were afraid to talk to each other as children.
At nineteen, Njoroge is pulled out of school to be interrogated by the police. Jacobo has been murdered, and they believe that Ngotho is involved. Njoroge is tortured mercilessly, but he refuses to give up any information. The police reveal that Ngotho has already confessed to the murder and that they have castrated him. During the torture, Njoroge passes out, and Mr. Howlands, who has been present at the interrogation, arranges for Njoroge to be released.
As it turns out, Ngotho did not commit the murder; he only confessed to help Kamau, who was being detained as a suspect. In fact, Boro killed Jacobo; he believed that it was the only way to avenge his brother's death in the war. Mr. Howlands eventually realized that Ngotho’s confession was false, but allowed him to be tortured anyway. However, he could not bring himself to execute Ngotho. Several days later, Ngotho dies. Njoroge and Boro visit him before he dies, and after Boro sees his father’s condition, he murders Mr. Howlands in the white man's home.
After Ngotho’s death, Njoroge is obliged to give up his education and to work in a dress shop. These events emotionally destroy Njoroge, and he goes to the one source of comfort he has left: Mwihaki. They admit that they love each other, but that they cannot be together because they are obliged to support their families, both of which are now missing a father. Njoroge tries to kill himself, but Nyokabi stops him and brings him home.