The Flight of Peter Fromm is a novel of ideas disguised as the biography of a young man from a Pentecostal fundamentalist background in Oklahoma, who loses his faith while a student at the University of Chicago Divinity School. His spiritual odyssey is narrated by his mentor, a professor at the divinity school - who is actually a humanist who believes neither in God nor in an afterlife. Although Peter never abandons his theism or his admiration for Jesus, he reaches a point where he feels it would be hypocritical to remain within the church and to become the evangelist he had hoped to be.

The counterpoint between Peter and the narrator reflects the eternal conflict between theism and atheism. In following the changes of Peter's beliefs, almost every aspect of Protestant theology and ethics is explored. The evolution of Peter's faith parallels the evolution of Christian theology, from the day of Pentecost to contemporary liberal theology.