As an example of a classical detective, Hercule Poirot moves through the action of Murder on the Orient Express with a self-assuredness that invites the reader to expect an ending typical of the genre. More often than not, classical detective novels conclude with the detective solving the case, the authorities apprehending the criminal, and harmony being restored to the community. Christie disrupts the conventions of this traditional structure, however, in order to examine what justice truly means. By putting an act of vigilantism at the heart of the mystery, she reverses the roles of the criminal and the victim. This choice forces both Poirot and the reader to grapple with the ethical implications of killing a killer, creating tension between the legal and moral dimensions of justice. Poirot ultimately makes a decision regarding this key question in the final moments of the novel, but until that point, his primary aim as the novel’s protagonist is to uncover the truth about Ratchett’s death. As an independent detective, Poirot has the ability to navigate the case on his own terms without the pressure of delivering a specific outcome. This freedom allows him to treat the mystery as a puzzle, and finding the true solution to the puzzle of Ratchett’s murder, regardless of the outcome, serves as the novel’s central conflict.

To establish the pursuit of truth as Poirot’s primary goal, Christie crafts an isolated setting and scenario that allows him to approach the mystery in an unbiased manner. The crime that inspires Poirot’s investigation and acts as the novel’s inciting incident, Mr. Ratchett’s murder, strangely appears to have no immediate impact on anyone beyond the dead man himself. This choice emphasizes the limited scope of the crime and allows Poirot to maintain an outsider’s perspective throughout. Christie further protects her detective from corruption by placing the investigation in a stranded train car. This choice not only cuts Poirot and the passengers off from the rest of the world, containing all the pieces of the crime in one location, it also adds to the sense that he is not anchored to the values of a particular group or place. The train exists in an in-between space as it travels from one country to another, and stopping it mid-journey leaves Poirot without a given set of laws to follow. Instead, this unique setting invites him to view all aspects of the mystery with an open mind. This perspective becomes crucial as he begins the process of investigating Ratchett’s death, especially as the details of the crime make it appear increasingly impossible. 

The rising action of the novel develops as Poirot interviews the passengers on the train and studies the physical evidence present at the scene of the crime, and the methodical way in which he approaches his investigation emphasizes a commitment to uncovering the truth. Unlike M. Bouc and Dr. Constantine, Poirot refuses to jump to conclusions about any of the passengers. He listens intently to each of them during their interviews and studies their behaviors in order to get a sense of who these individuals are. This emphasis on psychology over physical evidence alone enables Poirot to view the case in a more wholistic manner, a process which brings him closer to discovering the truth behind the crime than a more surface-level investigation would. He gets a sense of Mary Debenham’s calculating mind, for example, and this information ultimately allows him to determine how she fit into the puzzle of the crime. 

Once all of the evidence is in front of him, Poirot begins to see through the lies and misleading clues that the passengers offered him and, through a final round of questioning, uncovers the complicated reality of the case. The climax of the novel occurs at the genre-defying moment in which Poirot discovers that Ratchett’s killer is actually a group of people driven by a sense of moral obligation rather than an individual plagued by evil. Each of the passengers admit to their real identities as members of the Armstrong household, and they collectively express their desperation to punish Ratchett for his brutal murder of an innocent girl. 

Since the truth that Poirot finds is nowhere near the result he expected from his investigation, the subsequent step of ensuring justice becomes even more complex. He can either deliver the real solution to the police and condemn the passengers to jail, or he can lie and protect them knowing that their actions restored the social order that Ratchett’s crime destroyed. This question is the driving force behind the novel’s falling action as Poirot proposes two possible solutions, the real one and a false one, to the group assembled on the train. Poirot and M. Bouc’s final decision to lie to the police highlights Christie’s argument about the validity of moral acts of justice, even when those acts lead to a distortion of the truth.