Eugene Henderson is a troubled middle-aged man. Despite his riches, high social status, and physical prowess, he feels restless and unfulfilled, and harbors a spiritual void that manifests itself as an inner voice crying out I want, I want, I want . Hoping to discover what the voice wants, Henderson goes to Africa.
Upon reaching Africa, Henderson splits with his original group and hires a native guide, Romilayu. Romilayu leads Henderson to the village of the Arnewi, where Henderson befriends the leaders of the village. He learns that the cistern from which the Arnewi get their drinking water is plagued by frogs, thus rendering the water "unclean" according to local taboos. Henderson attempts to save the Arnewi by ridding them of the frogs, but his enthusiastic scheme ends in disaster, destroying the frogs but also the village's cistern.
Henderson and Romilayu travel on to the village of the Wariri. Here, Henderson impulsively performs a feat of strength by moving the giant wooden statue of the goddess Mummah and unwittingly becomes the Wariri Rain King, Sungo. He quickly develops a friendship with the native-born but western-educated Chief, King Dahfu, with whom he engages in a series of far-reaching philosophical discussions.
The elders send Dahfu to find a lion, which is supposedly the reincarnation of the late king, Dahfu's father. The lion hunt fails and the lion mortally wounds the king. Henderson learns shortly before Dahfu's death that the Rain King is the next person in the line of succession for the throne. Having no interest in being king and desiring only to return home, Henderson flees the Wariri village.
Although it is unclear whether Henderson has truly found spiritual contentment, the novel ends on an optimistic and uplifting note.