First and foremost, an Agatha Christie detective story or novel is a puzzle whose aim is to tickle the intellect. The author focuses upon facts about people, places, and events—the clues—that are needed to solve the puzzle, but in such a way as to challenge even the most perceptive reader. In other words, the writer of the traditional whodunit normally does not use the narrative as a means of delineating a theme or expounding upon an idea; such whodunits (written by Christie and most of her British contemporaries) thus differ from standard fiction, in which the presence of themes is the norm.

The works by Christie and her peers (those of the so-called Guilty Vicarage school), however, do have recurring characteristics that sometimes border on the thematic. For example, The Murder of Roger Ackroyd and similar mysteries usually take place in tranquil settings—such as upper-class English country homes—whose apparently peaceful normality suddenly is interrupted by murder. A private detective arrives on the scene and through his exceptional mental abilities purges the community of the evil that has disturbed it. Following the rooting out of the criminal, everything returns to a truly pure and idyllic state of normality, at least for a time. Because of this common progression in whodunits, some critics believe that the effect on readers may be similar to the catharsis that follows from classical tragedy.