Mrs. Hubbard is Linda Arden.

Mrs. Hubbard, the seemingly garrulous and slightly ridiculous American lady who dominates conversation on the Orient Express with tales of her daughter and her own nervous fears, is in fact Linda Arden, one of the greatest tragic actresses of her day and the mother of Sonia Armstrong. Her true identity is the hidden engine of the entire plot: she is the woman who, shattered by the kidnapping and murder of her granddaughter Daisy Armstrong and the subsequent deaths of her daughter and son-in-law, conceived and led the conspiracy of twelve to execute the man who escaped justice, Samuel Ratchett, alias Cassetti.

Identity and Disguise

Throughout the journey, Mrs. Hubbard presents herself as a fussy, slightly comical figure, a widow from America traveling to visit her daughter in Smyrna. She complains about the food, the currency, and the cold, and she is quick to share her intuitions, particularly her fear of the man in the next compartment, Ratchett. This performance is a deliberate and masterful act of concealment. Her true identity is Linda Arden, the mother of the late Mrs. Armstrong and the grandmother of the murdered child, Daisy. She is a woman of immense emotional force and theatrical skill, a fact she herself acknowledges when, after Poirot exposes her, she says in her natural voice, "I always fancied myself in comedy parts." Her disguise is so complete that even her own daughter's sister, Countess Andrenyi, does not recognize her, and she maintains the role of the slightly scatterbrained American to deflect any suspicion from her central role in the crime.

Role in the Conspiracy

Mrs. Hubbard's compartment, No. 3, which communicates directly with Ratchett's compartment, is the strategic heart of the murder plot. She is the only conspirator who cannot have a solid alibi, as her role requires her to be the point of entry for the other eleven executioners. She admits that her story about a man being in her compartment and the subsequent discovery of a Wagon Lit button were fabricated parts of the plan. Her performance was carefully rehearsed, though she made a critical error: she described the sponge-bag as masking the door bolt, a detail that would only be true in an even-numbered compartment, not her own odd-numbered one. This slip, which she later attributed to having rehearsed the scene in a different compartment on the outward journey, was one of the few flaws in an otherwise meticulously staged drama. She played the most important part, occupying the compartment that made her the most obvious suspect, trusting in her acting ability to carry her through.

Revelation and Confession

When Poirot presents his second solution, naming the twelve passengers as a self-appointed jury and identifying Mrs. Hubbard as the mastermind, she drops her disguise. In a "soft rich dreamy voice, quite unlike the one she had used throughout the journey," she confirms his deductions. She describes the day of the tragedy in New York, when she was "just crazy with grief," and explains how the plan was formed among the bereaved household and friends. She reveals that the idea of multiple stabbers came from the chauffeur, Antonio Foscarelli, and that the details were worked out by Mary Debenham and Hector MacQueen. She takes full responsibility, offering herself as the sole culprit, saying, "I would have stabbed that man twelve times willingly." Her confession is delivered with the full power of her theatrical voice, a voice that had once thrilled audiences, now used to plead for the others she calls "good faithful souls."

Thematic Significance

Mrs. Hubbard's dual identity embodies the novel's central conflict between legal justice and personal vengeance. As Linda Arden, she represents the raw, unassuageable grief of a mother and grandmother, a grief that transforms into a cold, calculated plan for retribution. Her performance as Mrs. Hubbard demonstrates that justice, in the absence of effective law, can be a theatrical act, staged and directed by those who have been wronged. Her final plea to Poirot—to lay the blame on her alone—underscores her role as the orchestrator and the one willing to bear the ultimate consequence for the collective act. Her character ultimately forces the question of whether a crime committed by a jury of the bereaved, in the name of a child who was failed by the legal system, can ever be considered murder.