Consider this description of mystery fiction from John Lanchester’s “The Case of Agatha Christie” in the London Review of Books.

Her career amounts to a systematic exploration of formal devices and narrative structures, all through a genre with strictly defined rules and a specified character list: a murder must happen, it must be solved by a detective, there must be a murderer, a victim, a set of characters who might be the murderer but turn out not to be, a number of possible motives, most of which turn out to be misleading; the setting must be circumscribed, the list of suspects finite, the motive and crucial evidence something disclosed to the reader but preferably not shown to be significant. And it must come in at around 50,000 words – that’s not a genre rule, it’s just how long Christie thought a murder story should be. . . . The elements of Christie’s fiction are all already in place: a country house, a finite list of suspects, the outsider detective intruding into a place of order and hierarchy that has been disrupted by a crime. . . . She isn’t much interested in the ethics or metaphysics of why people do the bad things they do. But she is unflinchingly willing to look directly at the truth that they do them. . . . Her sense of the world was that people do terrible things and suffer terrible consequences, and she took just enough of the truth of this to ground her fiction in a sense of reality, but never enough to unsettle the reader or disturb the genre frame. . . . In essence, that is what detective fiction is: a mystery about which of a particular cast of characters isn’t who they say they are. And that, I suggest, is a, perhaps even the, core reason for Christie’s appeal to so many readers in so many different times and places. Just as her work is formalist without being modernist, her preoccupation with identity, with the constructed nature of character and society, is a modernist preoccupation, expressed through a deliberately popular and accessible medium. Her work is a cocktail of orderly settings and deep malignity, of comfiness and coldness, and at its heart it asks one of the most basic questions of all, modernity’s recurring preoccupation: who are you?