Following the titular character, Moon Gaffney offers an intimate look at Irish-Catholic life in New York in the 1940s. Moon, a young lawyer with a bright future at Tammany Hall, finds himself constantly at odds with the world around him. The women in his life, his friends, and the expectations of his father lead him to question what social relationships are necessary for his Catholic practices. And his religious convictions and the pragmatism of his chosen vocation struggle incessantly at the back of his mind. When a politically charged case comes before him-defending black dock workers associated with a Communist group who have suffered a beating-Moon must choose to whom he will swear his fealty, the City of Man or the City of God. Moon's journey is further echoed in other characters of the novel as they each seek to live in harmony with the teachings of the Church and needs of the world around them.