Mystery and Crime Tropes

Christie's reputation as "The Queen of Crime" was built upon the large number of classic motifs that she introduced, or for which she provided the most famous example. Christie built these tropes into what is now considered classic mystery structure: a murder is committed, there are multiple suspects who are all concealing secrets, and the detective gradually uncovers these secrets over the course of the story, discovering the most shocking twists towards the end. Culprits in Christie's mysteries have included children, policemen, narrators, already deceased individuals, and sometimes comprise no known suspects (And Then There Were None) or all of the suspects (Murder on the Orient Express).

At the end, in a Christie hallmark, the detective usually gathers the surviving suspects into one room, explains the course of their deductive reasoning, and reveals the guilty party, although there are exceptions in which it is left to the guilty party to explain all (such as And Then There Were None and Endless Night).

Christie allows some culprits to escape earthly justice for a variety of reasons, such as the passage of time (retrospective cases), in which the most important characters have already died, or by active prescription. There are instances in which a killer is not brought to justice in the legal sense but does die as a direct result of their plot, sometimes by their own hand at the direction or with the collusion of the detective (usually Hercule Poirot).

However, stage, film, and television productions of some of her mysteries were traditionally sanitized with the culprits not evading some form of justice, for a variety of reasons – e.g., censors, plot clarity, and Christie's own changing tastes. In some stories, the question remains unresolved of whether formal justice will ever be delivered, such as Five Little Pigs and Endless Night. According to P. D. James, Christie often, but not always, made the unlikeliest character the guilty party. Savvy readers could sometimes identify the culprit by simply identifying the least likely suspect.