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. When Poirot realizes that Dr Willoughby and his institute have a connection to the Ravenscrofts, Poirot decides to solve both mysteries. Instead of immediately helping Mrs Oliver with the Ravenscroft case, Poirot instead chooses to investigate the murder of Dr Willoughby's father, which is a subplot that is not in the novel as a consequence, Dr Willoughby's character is greatly expanded.

Characters such as Mr Goby, Miss Lemon, George, Marlene Buckle (whose mother becomes Mrs Matcham's housekeeper) and ex-Chief Superintendent Spence were removed from the story (Spence's character is replaced with an original character named Beale), whilst the characters of Zélie Meauhourat and Mme Rouselle were combined.

The adaptation is generally faithful to the novel, except in a few instances. Poirot is absorbed by this case so Ariadne Oliver has to conduct the interviews of the elephants by herself. However a major side plot has been developed in which Dr Willoughby senior is murdered. The adaptation is fairly faithful to the original story insofar as the mystery of the death of the Ravenscroft is concerned. Mrs Oliver tries to incite Hercule Poirot to help her, but as he is busy with another case, she settles on playing the part of the amateur sleuth herself – after all, though a decade has passed since the tragedy, human memory is nearly as strong as that of elephants. Ariadne Oliver wishes to unravel the mystery behind the deaths of her goddaughter Celia's parents, who were found shot on their estate ten years prior.

Poirot elephants can remember