Dr. Edward Armstrong

Armstrong is accused of operating on a patient named Louisa Mary Clees while drunk, resulting in her death on the operating table. The accusation is delivered by a gramophone recording in the drawing room, publicly revealing his respectable Harley Street façade. He had never faced legal consequences for the act, as the medical profession of the era poorly policed itself, but the guilt followed him onto the island.

Armstrong is pushed off a cliff into the sea by Justice Wargrave, whose body is later washed ashore and found by the remaining survivors. Wargrave lured him into a private alliance, falsely claiming he had identified the murderer and needed Armstrong's help to expose them. Armstrong trusted Wargrave's judicial authority and walked willingly into the trap, making him arguably the most deceived victim on the island.

Armstrong trusts Wargrave because the judge represents the institutional authority Armstrong lost when his drunken surgery was exposed. Wargrave offers him a sanctioned role and the illusion of restored order, which Armstrong — driven by professional pride and unresolved guilt — cannot resist. His deference is rooted not in stupidity but in vanity and a desperate need to realign himself with respectable, official power.

Armstrong serves as the group's forensic authority, examining each corpse and determining the cause of death — potassium cyanide for Anthony Marston, chloral hydrate overdose for Ethel Rogers, and a syringe injection for Emily Brent. This medical role earns him credibility and status among the survivors, but it also deepens collective paranoia and places him near the centre of every investigation, increasing both his usefulness and his exposure to suspicion.

Armstrong speaks with General Macarthur and is visibly unsettled by the old soldier's serene acceptance of his impending death. Armstrong interprets Macarthur's calm as psychological collapse, but the exchange is ironic: Macarthur has accepted what Armstrong refuses to face — that none of them may leave the island alive. The conversation heightens Armstrong's own dread and foreshadows Macarthur's passive end.

With Lombard and Blore, Armstrong maintains an uneasy, suspicious alliance; the three search the island together but never achieve real trust, each privately considering the others potential suspects. With Wargrave, however, Armstrong drops his guard almost entirely. Lombard's cynical pragmatism and Blore's blunt suspicion clash with Armstrong's anxious professionalism, whereas Wargrave's judicial authority elicits the class- and profession-based deference that proves fatal.

Armstrong's body washing ashore is a pivotal shock that completely reorders the surviving characters' calculations. His earlier disappearance had already shattered trust among Vera, Lombard, and Blore — each privately suspected one of the others had killed him — so the corpse's reappearance forces them to revise every assumption about who can still be guilty, accelerating the novel's final collapse of suspicion and survival.

Armstrong embodies the danger of unacknowledged guilt combined with professional pride. Christie uses him to argue that social respectability and institutional authority can function as moral camouflage, shielding the guilty from accountability while leaving them psychologically vulnerable. His willingness to be manipulated by Wargrave illustrates the novel's broader theme: that guilt and self-interest can blind individuals to mortal dangers standing directly in front of them.