Dumb Witness

Wealthy spinster Emily Arundell writes to Hercule Poirot in the belief she has been the victim of an attempted murder after a fall in her Berkshire home. Her family and household believe she tripped over a ball left by her fox terrier, Bob. After Poirot receives the letter, he travels to Miss Arundell’s home, only to learn she is dead; her physician, Dr Grainger, states her death was from chronic liver problems. While recovering from her earlier fall, she made a new will, which bequeathed her vast fortune and home to her paid companion, Minnie Lawson.

Seeking to investigate Miss Arundell's belief that someone wanted to murder her, Poirot, accompanied by Captain Hastings, notes that under her previous will, her nephew Charles and nieces Theresa and Bella would have inherited. All three consider contesting the will.

Visiting the house on the pretence of buying it, Poirot discovers a nail covered with varnish at the top of the stairs and deduces a string had been tied to it. Through Miss Arundell's last words, he concludes that not only was Bob out all night, but also that Miss Arundell fell down the stairs as a result of a tripwire, and there is a chance Miss Arundell was indeed murdered. Her family, therefore, become suspects in the matter.

During his investigation, Poirot learns that a luminous aura was noticed coming from the dead woman's mouth when she spoke during a seance. Visiting Miss Lawson at her home, he learns that she saw someone moving about on the night of Miss Arundell's fall, who wore a brooch with the initials "TA." At the same time, Miss Lawson's gardener recalls Charles inquiring about his arsenic-based weed killer and is surprised to find the bottle containing it nearly empty.

Bella later leaves her Greek husband Jacob, on the implication he bullies her, taking the children with her. After Miss Lawson helps hide them in a hotel, Poirot moves her to another for fear of a second murder; before he does, he gives her a summary of Miss Arundell's death. The next day, Bella is found dead from an overdose of sleeping medication.

Bringing the surviving family members together, Poirot reveals Bella was the murderer. She hated her husband and sought to separate from him and keep her children in England. As she had no means to do so, she resolved to kill Miss Arundell to hasten her inheritance. When the attempt with the tripwire failed, she filled one of Miss Arundell's patent capsules with elemental phosphorus, knowing the poison would mimic the symptoms of liver failure. The aura witnessed by those attending the seance was due to the poison Miss Arundell had unknowingly consumed.

When she found out her aunt changed her will and that Poirot had discovered the cause of her death, Bella found herself in a far worse quandary. She relinquished her children to their father before committing suicide; the medication was originally intended to be used to murder Jacob, who was to be her second victim.

Poirot reveals that Miss Lawson saw Bella on the night of Emily's fall, though in a mirror; the brooch's initials were reversed from that of "AT" – Arabella Tanios. The arsenic was stolen by Theresa, who intended to use it, but could not bear to do so in the end. A small sum of cash that went missing was later discovered to have been stolen by Charles; he knew his aunt had changed her will before her death. Knowing Emily wished for no scandal, Poirot honours this, while Miss Lawson decides to share her inheritance with Theresa, Charles, and Bella's children. Meanwhile, Poirot and Hastings find themselves returning home with Bob joining them.