...as regards the Characters, the impossible-probable is better than the improbable-possible.
... the Christie characters were in many ways universal—so that an Icelander, for example, had no difficulty in recognizing his particular equiualent of Miss Marple in his Icelandic neighbor.
Tous les personnages d'Agatha Christie sont capables de tuer dans la mesure même où ils risquent d'être tués.
Brigitte Legars & Jean Thibaudeau
When classic detective fiction is attacked for its lack of reality, that attack usually begins with the form's characters. Puppets, cardboard cutouts, one-dimensional stereotypes, stock figures, plot pawns and pieces of a jigsaw puzzle are just a few of the epithets that have been used to dismiss the characters. Such name-calling evades the real question: what are the requirements of characterization in detective fiction? Since classic detective fiction is ultra-Aristotelian in placing action above character, it consists not of characters who determine the action, but action which determines the characters. Rather than existing as "real human beings," the characters follow conventional lines to accomplish the action of the plot, which is the discovery of one of them as a lawbreaker and the restoring of order to a society which has been disrupted by that person. This archetypal pattern underlying all of Christie's novels and stories does not allow for extensive psychological development of characters, for it would only impede the plot action. Dorothy Sayers has well stated the problem of realistic characters in detective fiction: "At some point or other, either their emotions make hay of the detective interest, or the detective interest gets hold of them and makes their emotions look like pasteboard." 1
The characters should behave like reasonably normal human beings. If they are utterly unbelievable, their actions will also be; if they are utterly dull, the reader will not care what they do. Though basically stereotypes (yes, admittedly they are), they can be made lively, fresh and amusing within the limits of the plot requirements, that is, they can be, what Auden calls, "aesthetically interesting." But the plot requirements must be the first consideration. Barzun