The book begins by describing the four main characters – Munira, Karega, Wanja, and Abdulla – just after the revelation that three prominent Kenyans, two businessmen and one educator, have been killed in a fire. The next chapter moves back in the novel's timeline, focusing on Munira's move to Ilmorog, to begin work as a teacher. He is initially met with suspicion and poor classroom attendance, as the villagers think he will give up on the village soon, in much the same way previous teachers have done. However, Munira stays and, with the friendship of Abdullah, another immigrant to Ilmorog who owns a small shop and bar, carves out a life as a teacher.
Soon Wanja arrives, the granddaughter of the town's oldest and most revered lady. She is an attractive, experienced barmaid who Munira begins to fall in love with, despite the fact he is already married. She too is escaping the city, and begins to work for Abdullah, quickly reshaping his shop, and expanding its bar. Karega arrives in Ilmorog to seek Munira to question him about their old school Siriana. After a brief relationship with Munira, Wanja once again grows disillusioned and leaves Ilmorog. The year of her departure is not good for the village as the weather is harsh and no rains come, making for a poor harvest. In an attempt to enact changes, the villagers are inspired by Karega to journey to Nairobi in order to talk to their Member of Parliament.
The journey is very arduous and Joseph, a boy that Abdullah had taken in as his brother and who had worked in his shop, becomes ill. When they arrive in Nairobi, the villagers seek help from every quarter. They are turned away by a reverend who thinks they are merely beggars, despite their pleas of help for the sick child. Trying at another house, some of the villagers are rounded up and forced into the building where they are questioned by Kimeria, a ruthless businessman who reveals that he and their MP are in league with one another. He blackmails Wanja, and subsequently rapes her. Upon arriving in Nairobi and speaking to their MP, the villagers realise that nothing will change, as he is little more than a demagogue. However, they do meet a lawyer who wishes to help them and others in the same predicament and through a court case highlights Ilmorog's plight. This draws attention from national press and donations and charities pour into Ilmorog.
Finally, the rains comes, and the villagers celebrate with ancient rituals and dances. During this time, Karega starts a correspondence with the lawyer that he met in Nairobi, wishing to educate himself further. To celebrate the rain's coming, Nyakinyua brews a drink from the Thang'eta plant, which all of the villagers drink. Karega tells the story the love between him and Mukami, the older sister of Munira. Mukami's father looked down on Karega because of his brother's involvement with the Mau Mau. Forced to separate, Mariamu and Karega do not see each other again, and Mukami later commits suicide by jumping into a quarry. This is the first time Munira hears the story. Later, an unknown plane crashes in the village; the only victim is Abdulla's donkey. Wanja notices that there are several large groups of people who come to survey the wreckage, and suggests to Abdulla that they begin to sell the Thang'eta drink in Abdulla's bar. The drink attracts notoriety, and many people come to the bar in order to sample it. Out of fury for Karega's connection to his family and jealousy of his relationship with Wanja, Munira schemes to have Karega fired from his teaching post with the school. Karega then leaves Ilmorog.
Development arrives in Ilmorog as the government begin to build the Trans-Africa road through the village, which brings an increase in trade. Karega returns to Ilmorog, telling of his slow spiral into alcoholism before finally securing work in a factory. After getting fired from the factory, he returns to Ilmorog. The change in Ilmorog is rapid, and the villages changes into the town of New Ilmorog. The farmers are told that they should fence off their land and mortgage parts of it to ensure that they own a finite area. They are offered loans which are linked to their harvest turnout to pay for this expense. Nyakinyua dies and the banks move to take her land. To prevent this Wanja sells her business and buys Nyakinyua's land. She opens up a successful brothel in the town, and is herself one of the prostitutes. Munira goes to see her to attempt to rekindle their romance, but is met with only a demand for money. He pays, and the couple have sex. Karega goes to see Wanja who both still have strong feelings for each other, but after disagreeing about how to live he leaves. Wanja plans to separate herself finally from the men who have exploited her during her life, wanting to bring them to her brothel with all of her prostitutes sent away so that she could present the downtrodden but noble Abdulla as her chosen partner. Meanwhile, Munira is watching the brothel, and sees Karega arrive, and then leave. In a religious fervour, he pours petrol on the brothel, sets it alight, and retreats to a hill to watch it burn. Wanja escapes but is hospitalized due to smoke inhalation; the other men Wanja had invited died in the fire. Munira is sentenced with arson; later, Karega learns that the corrupt local MP was gunned down in his car whilst waiting for his chauffeur in Nairobi.
Explanation of the novel's title
The title Petals of Blood is derived from a line of Derek Walcott's poem 'The Swamp'. The poem suggests that there is a deadly power within nature that must be respected despite attempts to suggest by humans that they live harmoniously with it.
|“||Fearful, original sinuosities! Each mangrove sapling
Serpent like, its roots obscene As a six-fingered hand, Conceals within its clutch the mossbacked toad, Toadstools, the potent ginger-lily, Petals of blood, The speckled vulva of the tiger-orchid; Outlandish phalloi Haunting the travellers of its one road.
—Derek Walcott, The Swamp
Originally called 'Ballad of a Barmaid', it is unclear why Ngugi changed the title before release. The phrase "petals of blood" appears several times throughout the novel, with varying associations and meanings. Initially, "petals of blood" is first used by a pupil in Munira's class to describe a flower. Munira quickly chastises the boy, saying that 'there is no colour called blood'. Later, the phrase is used to describe flames, as well relating to virginity during one of Munira's sexual fantasies.