Fifth Business is crafted as a memoir. Upon his retirement from Colborne College, a condescending article about Dunstan Ramsay's farewell dinner is published in the College Chronicle under the title "Farewell to the Cork." Notably, this brief piece is the sole instance in the novel where the nickname "Corky" is used. Although many students and colleagues likely referred to Ramsay by this nickname, it is not his preferred name. Ramsay writes this memoir for the headmaster of Colborne to set the record straight and counter the misleading portrayal of his life presented in the article.

This novel diverges from traditional first-person narratives like The Great Gatsby (Fitzgerald, 1925) because the narration primarily focuses on the narrator himself rather than the events or people he describes. The book is segmented into six chapters: "Mrs. Dempster," "I Am Born Again," "My Fool-Saint," "Gyges and King Candaules," "Liesl," and "The Soiree of Illusions." Ramsay outlines his life journey, dividing it into six phases, each represented by a person or experience that encapsulates the essence of that period. Critics often highlight the presence of Jungian archetypes in Davies's work. These archetypes are not superimposed but naturally arise from the narrative elements presented in the story.

The life of Boy Staunton is depicted alongside Dunstan Ramsay's. While Staunton appears to undergo significant changes throughout the novel, his internal growth does not parallel his external successes in wealth and status. In contrast, Ramsay seems to remain static, dedicating his life to a single pursuit. However, the novel chronicles his psychological exploration and development, revealing that the Dunstan Ramsay at sixty is not someone who wishes he "could get into a car and drive away from the whole damned thing," unlike Staunton, who harbors such a desire near the novel's conclusion.

Fifth Business starts on December 27, 1908, in Deptford, Ontario. An incident occurs that triggers a series of events, which conclude in October 1968 in Toronto with the mysterious death of Boy Staunton, one of Canada's wealthiest men. The novel, crafted as a memoir, follows the lives of three individuals connected to the 1908 event. Boy Staunton, one of these characters, achieves great material success by embracing the principles of wealth and materialism as advocated by George Maiden Leadbeater. Despite his accomplishments, Staunton perpetually seeks to expand his economic empire and continuously raises the benchmarks of his success throughout his life.

In contrast, Dunstan Ramsay, a contemporary of Staunton, leads a different kind of existence. He becomes a history teacher and remains in the same position for forty-five years. Alongside his teaching career, he publishes works in his field of hagiography—the biographies of saints or other idealized figures—focusing on the intersections of history and myth. Due to the lack of academic respectability for his specialty, it remains somewhat of a personal passion rather than a professional pursuit. The third person involved in the incident is Mrs. Amasa Dempster, the wife of a Baptist minister. Her life appears to be profoundly altered by the 1908 event. The residents of Deptford come to view her as simple-minded, and she eventually ends up in an insane asylum, where she passes away in 1959. While it is never entirely clear if Mrs. Dempster's emotional issues stem from the incident, for Dunstan Ramsay, they do, and he feels responsible for her fate.

This novel does not focus on specific social issues but rather on an individual's self-understanding and their place in the world. Each character has their own way of navigating life. Boy Staunton seemingly conquers the world but never truly understands it, himself, or those around him. Dunstan Ramsay is cast in the role of Fifth Business, a term from drama or opera referring to a character essential to the plot but not part of the main action. Most people view him as an observer, someone who watches life unfold without participating. This novel, presented as Ramsay's personal memoir, aims to correct that misconception. Lastly, Mrs. Dempster seems to have a distinct understanding of her surroundings, but her perspective differs from others, leading her neighbors to consider her mad.

Robert Browning's The Ring and the Book (1868-1869) serves as a fundamental source for Davies's narrative approach in this novel. In Browning's poem, the same events are depicted from multiple perspectives. Davies advances this idea by having his narrator recount his own story. The plot we uncover is secondary to the insights we gain about the character. Patricia Merivale has observed that, aside from being Dunstan Ramsay's autobiography, Fifth Business also functions as "Dunstan's 'lives' of the 'saints.'" She connects the novel to two elegiac romances: Hugh MacLennan's The Watch That Ends the Night (1959) and Thomas Mann's Dr. Faustus (1947), as well as Thomas Mann's "ironic Saint's Life," The Holy Sinner (1951).

Michael Peterman identifies several significant predecessors to Fifth Business. He highlights similarities between this novel and John Henry Newman's religious autobiography Apologia Pro Vita Sua (1864). Like Newman, Ramsay is providing a defense or justification for his life, as he responds to Lorne Packer's condescending tribute to "Corky" in the College Chronicle, which implied that Ramsay's historical approach was imaginative and outmoded. Peterman also draws parallels with J. B. Priestly's The Magicians (1954) and Iris Murdoch's A Severed Head (1961). He notes that Sir Charles Ravenstreet's dilemma in The Magicians between "the power-wielding businessman Mervil" and "the three enigmatic magicians, Wayland, Marot, and Perperak" mirrors Ramsay's struggle "between the materialistic world of Boy Staunton and the spiritual domain of Mary Dempster." Additionally, Honor Klein in A Severed Head plays a role similar to Liesl in terms of appearance and guidance.

Fifth Business serves as the opening installment of the Deptford trilogy, a series of three interconnected novels. The Jungian psychology subtly introduced in this first book is fully explored in The Manticore (1972), which delves into the psychoanalysis of Boy Staunton's son, David. The final novel, World of Wonders (1979), centers on Magnus Eisengrim and his traveling magic show.