Elephants Can Remember

At a literary luncheon, Ariadne Oliver is approached by Mrs Burton-Cox, whose son Desmond is engaged to Oliver's goddaughter Celia Ravenscroft. Mrs Burton-Cox questions the truth regarding the deaths of Celia's parents. Twelve years before, Oliver's close school friend Margaret Ravenscroft and her husband, General Alistair Ravenscroft, were found dead near their manor house in Overcliffe. Both had been shot with a revolver found between their bodies, which bore only their fingerprints. The investigation into their deaths could not determine if it was a double suicide, or if one of them murdered the other and then committed suicide. Their deaths left Celia and another child orphaned. After consulting Celia, Mrs Oliver invites Hercule Poirot to investigate.

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.

Poirot soon turns his attention to the Burton-Cox family, and learns that Desmond was adopted and knows nothing about his birth mother. Through his agent, Mr Goby, Poirot learns that Desmond is the illegitimate son of a deceased actress, Kathleen Fenn, who once had an affair with Mrs Burton-Cox's husband and who bequeathed a considerable fortune to Desmond, to be held in trust until he was of age or had married, and which would go to his adoptive mother if he died. Poirot suspects that Mrs Burton-Cox wants to prevent the marriage of Desmond and Celia in order to maintain the use of the money, but he finds no suggestion that Mrs Burton-Cox wishes to kill her son. 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.

Poirot reveals that the woman who died with Alistair was not his wife but her twin, Dorothea. A month before the deaths she had fatally injured Margaret and Margaret had made her husband promise to protect her sister from arrest. Alistair had Zélie help him to conceal the truth of his wife's death by planting her body at the foot of a cliff and fabricating the story that it was Dorothea who had died, then having Dorothea take the place of his wife. While she fooled the Ravenscrofts' servants, the family dog could not be deceived and thus bit her. 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. Knowing the facts, Desmond and Celia can face the future together.