Poirot and Mrs Oliver proceed to meet elderly witnesses associated with the case, whom they dub "elephants", and discover that Margaret Ravenscroft owned four wigs; that the Ravenscrofts' dog was devoted to the family, but bit Margaret a few days before her death; that Margaret had an identical twin sister, Dorothea, who had spent time in a number of psychiatric nursing homes, and was believed to have been involved in two violent incidents in Asia, including the drowning of her infant son after the death of her husband; and that a month before the couple died Dorothea had been sleepwalking and had died after falling off a cliff.

Later Poirot learns the names of governesses who served the Ravenscroft family, one of whom, Zélie Meauhourat, travelled to Lausanne after the couple's deaths.

Eventually he begins to suspect the truth about the Ravenscrofts' death and asks Zélie to return to England to help him to explain it to Desmond and Celia.

A month after his wife's death Alistair murdered Dorothea to prevent her from injuring anyone else, making certain that she held the revolver before she was killed, and then he committed suicide.

The "Elephants" Maurice Richardson in The Observer of 5 November 1972 called the novel "A quiet but consistently interesting whodunnit with ingenious monozygotic solution.

Acres of meandering conversations, hundreds of speeches beginning with 'Well, …' That sort of thing may happen in life, but one doesn't want to read it.

The sharp drops in size of vocabulary and the increases in repeated phrases and indefinite nouns suggested that Christie may have been suffering from some form of late-onset dementia, perhaps Alzheimer's disease.

This subplot also includes an original character named Marie McDermott, an Irish-American girl who works as Dr Willoughby's filing clerk and turns out to be his mistress.

The character is ultimately revealed to be Dorothea Jarrow's daughter, who is avenging her mother for the cruel treatments she experienced at the hands of Professor Willoughby (an entirely fictional version of hydrotherapy), and also for her mother's murder (as she was at Overcliffe on the day of the tragedy and overheard General Ravenscroft make his plans) by trying to kill both Celia and Desmond.

Zélie spirited her away to Canada after the tragedy, and she had to wait thirteen years before she could earn enough money to travel to England and exact her revenge.