Ezeulu, the chief priest of Ulu, notices his influence waning due to pressures from within his community and from outside forces. The British aim to solidify their dominance over the Igbo by promoting Christianity and building roads. At the same time, the Igbo community, caught up in petty rivalries, unintentionally aids the British. This is evident when Ezeulu's efforts to keep peace with the Okperi are thwarted by the assertive and powerful Nwafo, resulting in the British settling the dispute in Okperi's favor.

Colonialism has unleashed forces that are beyond the control of individuals on either side. Ezeulu has successfully maintained a friendly relationship with Captain Winterbottom. However, as Winterbottom grows older and becomes ill, he increasingly hands over his duties to the less insightful Clarke and Wright. These men, who spend their nights drinking and ridicule Winterbottom, even mock his moral stance against sleeping with "native" women. On both sides, shallow and less ethical men are taking the place of the wiser and more cautious older men. Winterbottom's serious illness, which requires hospitalization just before Ezeulu's arrest, seems far from coincidental.

Similar to his earlier work, Things Fall Apart (1958), Achebe demonstrates how both the Igbo's traditional beliefs and British Christianity yield under the strain of real-world events. Oduchi's harsh treatment of the python acts as a warped reflection of Christian teachings, leading to unforeseen consequences. In contrast, Ezeulu's strategy to use his youngest son as an informant within the Christian community fails due to Oduchi's unexpected and intense commitment. Despite this, Ezeulu displays notable integrity, akin to Captain Winterbottom, though to a lesser degree. Ezeulu's unwavering adherence to the literal practice of eating the yams is driven not by pride but by his devotion to Ulu and a strong desire to remain resolute amid widespread disintegration.

The ultimate betrayal, symbolized in part by the death of his beloved son Obiko at the hands of the god he has loyally worshipped, pushes Ezeulu into madness by the novel's conclusion. The narrator sees this madness as somewhat of a blessing, as it lets Ezeulu exist without disturbance from his community, most of whom have embraced Christianity. In contrast, the recovery and good health of Winterbottom, who did nothing to assist Ezeulu, underscore the uneven impact colonial rule has had on Africans.

Opportunism, whether intentional or not, frequently appears in Achebe's writings, as illustrated by John Goodcountry, an African Anglican Christian priest. Goodcountry exploits the postponed yam harvest to oppose both Ulu and Ezeulu. With the threat of the yams rotting in the fields and the villagers facing starvation, Goodcountry offers Christian absolution to those who ignore Ezeulu's command and harvest the yams regardless. Most of the villagers agree to this. The book ends with the line: "Thereafter any yam harvested in his fields was harvested in the name of the son." This line underscores the ironic triumph of Christianity while also echoing the theme of a father's betrayal. The tone of the ending is reflected in Achebe's dedication of the book to his father.