Before the First World War, crime fiction was popular, but often associated with lurid and chaotic events far removed from the experience of the average reader. By contrast, a new and highly formulaic genre of crime writing became popular in the 1920s and 1930s. These cozy mysteries, or “whodunits,” presented the facts of the crime like tidy puzzle boxes, and often took place in remote, enclosed locations uncontaminated by the chaos of the outside world. In his “Ten Commandments” for crime writing, written in 1929, the essayist Ronald Knox wrote that a good crime story “must have as its main interest the unraveling of a mystery; a mystery whose elements are clearly presented to the reader at an early stage in the proceedings, and whose nature is such as to arouse curiosity, a curiosity which is gratified at the end.” Agatha Christie’s novels were the genre’s exemplars.

The meticulously crafted mysteries of this era run on a strict narrative path, each stop of which must be visited before their characters or themes are considered seriously. Each must present at least the illusion of clarity in presentation of the facts so that the reader can have the fun of attempting to guess the criminal before they are revealed at the end.