The Fourth Deadly Sin belongs to a subgenre of the mystery story called the "police procedural," which focuses on professional police methods to solve crimes. Typically, they emphasize the seamier, more physically demanding aspects of everyday life within a community, usually a large city.

Thus, The Fourth Deadly Sin touches on police brutality, sexual dysfunctions, adultery, homosexuality, and greed, and features characters such as thugs, prostitutes, psychotic Vietnam War veterans, inner-city priests, as well as a cross-section of society: homeless, butchers, clerical workers, government employees, and rich psychologists. The social ills presented by the novel serve primarily as background to the solving of the mystery and are not discussed in depth.

Mental illness is presented in some detail because the novel's mystery focuses on the murder of a psychiatrist, probably by one of his patients. Six of his patients are presented, each with his...