The play is set in post-colonial Kenya. Kĩgũũnda and his wife Wangeci, two poor peasants, are waiting for a visit from the wealthy Kĩoi and his wife, Jezebel. While they are waiting they argue with their daughter, Gathoni, who they believe to be to lazy and disrespectful on account of being influenced by modernity.
Two of their friends, Gĩcaamba and his wife Njooki, stop by before the visit. Gĩcaamba is very radical, and speaks of how oppressed the Kenyan people are by the Kenyan authorities and the foreigners with whom they collaborate, as well as the deleterious Western religions that infiltrate their land. He decries the wealthy and their avarice, and how they consistently take from the poor to line their own pockets.
Gĩcaamba and Njooki leave as Kĩoi and his wife arrive. Wangeci and Kĩgũũnda secretly wonder if they are there because Gathoni is romantically involved with Kĩoi and Jezebel’s son, John. Kĩoi and Jezebel, as well as two other upwardly-mobile Africans, Ndugĩre and his wife Helen, sit down and begin to inform Kĩgũũnda and Wangeci that they need to have a lawful Christian marriage and join the church. They are both hesitant, and Kĩgũũnda practically shouts them out of his hut.
After they leave, Kĩgũũnda and Wangeci think about what the rich man and his wife said. Eventually Wangeci comes to believe that they want the marriage because then it would be fine for Gathoni and John to marry. Kĩgũũnda agrees, and they plan to go to Kĩoi’s house to tell them they agree with the plan.
Before they go, Gĩcaamba and Njooki return and warn them about throwing their lot in with those people. Gĩcaamba says Kĩoi ought to have come with a wage increase, not with an invitation to join the Christian church. He says his friends’ marriage in valid because it was done in the Kenyan way. Gĩcaamba urges them to remember how Christians were complicit with the enemies of the Kenyan people during the independence struggle.
Kĩgũũnda and Wangeci ignore these entreaties and decide to go to Kĩoi’s house. They arrive and are treated rudely by Jezebel, not being allowed to eat with them, but when they announce their desire to have a Christian wedding, the rich couple is pleased.
Kĩgũũnda and Wangeci say they are happy to do this but have no money, and wonder if they can borrow a bit to pay for the ceremony and reception. Kĩoi and Jezebel laugh and say Kĩgũũnda is wealthy because he gets paid more than others and has a title deed to one and a half acres. Kĩoi finally says he will insure a loan at the bank for Kĩgũũnda, using the title deed as collateral.
Kĩgũũnda and Wangeci are happy, and buy a lot of things for their house and for the wedding. They imagine the ceremony in their heads, but it all comes crashing down when Gathoni returns and cries that she is pregnant but John has jilted her.
They go to Kĩoi, assuming he will want the children to marry, but he viciously calls Gathoni a whore and says John is guilty of nothing. Kĩgũũnda is enraged and pulls out a sword he wears under his clothing. He threatens Kĩoi, who cowers in fear, but a home guard and Jezebel enter the house, with Jezebel brandishing a gun. She orders them to leave, and as Kĩgũũnda and Wangeci turn to go, Kĩgũũnda turns back for his sword and is shot by Jezebel.
After this incident, Wangeci wails to Gĩcaamba and Njooki about her family’s troubles. Gathoni has left to become a barmaid, and Kĩgũũnda, recovered from being shot, is drunk and depressed. It seems that Kĩoi used his powers at the bank to call in the loan, which took away their title to their land, and then bought it himself so a foreign company could build a factory on it. Kĩgũũnda comes back from the bar and is angry, fighting with Wangeci.
Gĩcaamba says they must not fight amongst themselves, but instead rise up against their oppressors. All sing and pledge themselves to wake up, to fight back. They proclaim that the trumpet of the masses, of the poor, has been blown.