Wanja is the main female character in the novel, one of the four protagonists accused of murder. When she was in school, she was seduced by Hawkins Kimeria, a wealthy man, and became pregnant. She abandoned the baby in a drain, carrying this guilt with her always. She moves to Ilmorog to be with her grandmother and starts a successful business as a distiller, but she's not allowed to keep it. She then becomes a high-paid prostitute.

Wanja tries to find her place in the new society of Kenya after its independence from the British. She's an intelligent woman  who is desired by all of the main male characters. She has an affair with Karega, a student activist, who cares a great deal about her. Godfrey Munira becomes so jealous of Wanja's affair with Karega, Munira fires Karega. All of the men want her, and many of their actions are motivated by their desire for her.

After Wanja is forced to become a prostitute, she sees Ilmorog change from a place of peace and beauty to an industrial town where the values of the small village are eroded. She remarks that Kenya has become a place where "You eat somebody or you are eaten. You sit on somebody or somebody sits on you."