The novel opens with the trial of Obi Okonkwo on the charge of accepting a bribe. It then jumps back in time to a point before his departure for England and works its way forward to describe how Obi ended up on trial.
The members of the Umuofia Progressive Union (UPU), a group of Igbo men who have left their villages to live in major Nigerian cities, have taken up a collection to send Obi to England to study law, in the hope that he will return to help his people navigate British colonial society. But once there, Obi switches his major to English and meets Clara Okeke for the first time during a dance.
Obi returns to Nigeria after four years of studies and lives in Lagos with his friend Joseph. He takes a job with the Scholarship Board and is almost immediately offered a bribe by a man who is trying to obtain a scholarship for his little sister. When Obi indignantly rejects the offer, he is visited by the girl herself, who implies that she will bribe him with sexual favors for the scholarship, another offer Obi rejects.
At the same time, Obi is developing a romantic relationship with Clara Okeke, a Nigerian woman who eventually reveals that she is an osu, an outcast by her descendants, meaning that Obi can not marry her under the traditional ways of the Igbo people of Nigeria. He remains intent on marrying Clara, but even his Christian father opposes it, although reluctantly due to his desire to progress and eschew the "heathen" customs of pre-colonial Nigeria. His mother begs him on her deathbed not to marry Clara until after her death, threatening to kill herself if Obi disobeys. When Obi informs Clara of these events, Clara breaks the engagement and intimates that she is pregnant. Obi arranges an abortion, which Clara reluctantly undergoes, but she suffers complications and refuses to see Obi afterwards.
All the while, Obi sinks deeper into financial trouble, in part due to poor planning on his end, in part due to the need to repay his loan to the UPU and to pay for his siblings' educations, and in part due to the cost of the illegal abortion.
After hearing of his mother's death, Obi sinks into a deep depression and refuses to go home for the funeral. When he recovers, he begins to accept bribes in a reluctant acknowledgement that it is the way of his world.
The novel closes as Obi takes a bribe and tells himself that it is the last one he will take, only to discover that the bribe was part of a sting operation. He is arrested, bringing us up to the events that opened the story.