Colonel Armstrong is Daisy Armstrong's father.

Colonel Armstrong was the father of Daisy Armstrong, the three-year-old girl whose kidnapping and murder by Cassetti (the man who later traveled under the alias Samuel Edward Ratchett) set in motion a chain of tragedies that ultimately led to a collective act of vengeance on the Orient Express. A decorated officer who had won the Victoria Cross, Armstrong was described by those who knew him as a "nice fellow" and "everybody liked him." His marriage to Sonia Armstrong, the daughter of the celebrated actress Linda Arden, produced one child, Daisy, whom they idolized. The kidnapping shattered their lives: after the parents paid an enormous ransom of two hundred thousand dollars, the child's dead body was discovered, having been dead for at least a fortnight. The shock caused Mrs. Armstrong, who was expecting another baby, to give birth prematurely to a stillborn child; she herself died. Her broken-hearted husband shot himself. The tragedy did not end there: the French nursemaid, Susanne, who was wrongly suspected of complicity, threw herself from a window in despair and was killed. Colonel Armstrong's closest friend, Colonel Arbuthnot, who had served with him in the war, was present in New York during that awful time and became one of the twelve who decided that Cassetti must die. The colonel's death left his mother-in-law, Linda Arden, "crazy with grief," and his household—including the chauffeur Antonio Foscarelli, the nurse Greta Ohlsson, the governess Mary Debenham, and the valet Masterman—united in a shared determination to carry out the sentence that the law had failed to deliver.

Identity and Background

Colonel Armstrong was an Englishman who held the Victoria Cross, a fact that testified to his bravery and distinguished military service. He was half American, his mother having been a daughter of W. K. Van der Halt, the Wall Street millionaire. He married Sonia Armstrong, the daughter of Linda Arden, the most famous tragic American actress of her day. The couple lived in America and had one child, a girl named Daisy, whom they adored. Armstrong's social circle included Princess Dragomiroff, who was a close friend of Linda Arden and became godmother to Sonia Armstrong. The colonel's character was such that he inspired deep loyalty: his batman in the war, Edward Masterman, later became his valet in New York, and his friend Colonel Arbuthnot described him as a man who "had a very distinguished career."

The Armstrong Kidnapping Case and Its Aftermath

When Daisy Armstrong was three years old, she was kidnapped, and an impossibly high sum was demanded for her return. The parents paid the enormous ransom of two hundred thousand dollars, but the child's dead body was discovered; it had been dead for at least a fortnight. The public indignation rose to fever point. The shock of the discovery caused Mrs. Armstrong, who was expecting another baby, to give birth prematurely to a dead child; she herself died. Her broken-hearted husband shot himself. The French nursemaid, Susanne, was wrongly suspected of complicity; the police refused to believe her hysterical denials, and in a fit of despair she threw herself from a window and was killed. It was proved afterward that she had been absolutely innocent. About six months later, Cassetti was arrested as the head of the gang, but by means of his enormous wealth and the secret hold he had over various persons, he was acquitted on a technical inaccuracy. He changed his name to Ratchett and left America, traveling abroad as a gentleman of leisure.

The Conspiracy and Its Motivation

Colonel Armstrong's death was the catalyst that transformed grief into a planned act of justice. His mother-in-law, Linda Arden, later described that "awful day in New York" when she was "just crazy with grief; so were the servants. And Colonel Arbuthnot was there too. He was John Armstrong's best friend." The decision was made then and there that the sentence of death that Cassetti had escaped had to be carried out. There were twelve of them—or rather eleven, since Susanne's father, Pierre Michel, was in France. The chauffeur, Antonio Foscarelli, suggested the method of multiple stab wounds, and Mary Debenham worked out the details later with Hector MacQueen, whose father had been the district attorney who handled the case. The plan took a long time to perfect: they tracked Ratchett down, placed Masterman and MacQueen into his employment, and arranged for Pierre Michel, Susanne's father, to be the conductor on the Orient Express. The twelve passengers in the Stamboul-Calais coach—each connected to the Armstrong household—became a self-appointed jury, and Colonel Armstrong's memory, along with the deaths of his wife, his child, and the unborn baby, provided the moral authority for their act.

Narrative Role and Significance

Colonel Armstrong's role in the story is that of the absent victim whose suffering justifies the conspiracy. He never appears alive in the narrative, but his death—along with those of his wife and child—is the emotional and moral foundation upon which the entire plot rests. The revelation of his identity as the father of the murdered child transforms the investigation: Poirot's discovery of the charred note fragment mentioning "little Daisy Armstrong" leads him to identify Ratchett as Cassetti, and from there to uncover the connections among the passengers. The colonel's military honor, his tragic end, and the loyalty he inspired in those who served him create a portrait of a man whose life was destroyed by a crime that the legal system failed to punish, and whose memory became the rallying point for a collective act of vengeance.