Hector MacQueen's father was the district attorney for the Armstrong case.

Hector MacQueen's father was the district attorney who handled the Armstrong kidnapping case, a fact that directly links MacQueen to the central tragedy that drives the murder of Samuel Edward Ratchett. This connection provides MacQueen with a deeply personal motive for joining the conspiracy of twelve passengers who execute Ratchett on the Orient Express.

Identity and Background

Hector MacQueen is a young American who served as Ratchett's secretary and courier for just over a year. He met Ratchett in Persia after a failed oil concession venture and accepted the well-paid position. MacQueen is articulate, intelligent, and initially presents himself as a detached employee who disliked his employer without specific reasons. However, his true background emerges during Poirot's investigation: his father was the district attorney who prosecuted Cassetti, the man who kidnapped and murdered three-year-old Daisy Armstrong. MacQueen reveals this when Poirot discloses Ratchett's true identity, stating, "My father was the district attorney who handled the case, Mr. Poirot. I saw Mrs. Armstrong more than once—she was a lovely woman. So gentle and heartbroken." This revelation transforms MacQueen from a mere secretary into a figure with a direct emotional stake in the Armstrong tragedy.

Role in the Conspiracy

MacQueen's position as Ratchett's secretary was not accidental but part of the carefully orchestrated plan. He was instrumental in ensuring Ratchett traveled on the Orient Express on the night Pierre Michel was on duty, and he managed the logistics of the conspiracy. During the investigation, MacQueen twice emphasizes that Ratchett could not speak French, a detail that Poirot later recognizes as a deliberate clue planted to mislead. MacQueen also destroys the real threatening letters and substitutes artificial ones, and he is the one who communicates to the other conspirators that the charred note fragment mentioning "Armstrong" has been discovered. His role requires him to provide an alibi for Colonel Arbuthnot and to appear cooperative while steering suspicion away from the group.

Relationships and Conflict

MacQueen's relationship with Ratchett is one of concealed hatred masked by professional efficiency. He admits to Poirot that he "disliked and distrusted" Ratchett, believing him to be "a cruel and dangerous man." This animosity is rooted in his father's prosecution of the Armstrong case and his own emotional response to the tragedy. MacQueen's relationship with the other conspirators is one of shared purpose; he works closely with Mary Debenham, who "worked out all the details later with Hector MacQueen," and with Linda Arden, who notes that MacQueen "had always adored Sonia—my daughter—and it was he who explained to us exactly how Cassetti's money had managed to get him off." His loyalty to the group is absolute, and he willingly risks his own safety to protect the others.

Change and Ending

Throughout the investigation, MacQueen maintains a facade of innocence, but his composure cracks when Poirot reveals the charred note. His initial reaction—"But surely—" followed by a pause and a revised statement—betrays his knowledge that the note should have been destroyed. In the final confrontation, MacQueen's role is fully exposed as part of the "jury of twelve" that condemned Ratchett. He does not confess but accepts Poirot's solution without protest. His fate is left to the discretion of M. Bouc and Dr. Constantine, who agree to present the first, false solution to the authorities, allowing MacQueen and the others to escape legal consequences.

Thematic Significance

MacQueen's involvement embodies the theme of justice versus law. His father, as district attorney, represented the legal system that failed to convict Cassetti. MacQueen himself becomes an instrument of extra-legal vengeance, using his position to facilitate a private execution. His character illustrates how the failure of institutional justice can drive individuals to take the law into their own hands, and his personal connection to the Armstrong case underscores the emotional weight that motivates the conspiracy. MacQueen's transformation from a detached secretary to a committed conspirator highlights the power of grief and the desire for retribution to override personal safety and professional ethics.