Audiobook Title:
Elephants Can Remember (Unabridged)
By: Agatha Christie

This was followed by the grisly discovery of two more bodies, a husband and wife, shot dead. But who had killed whom? Was it a suicide pact? A crime of passion? Or cold-blooded murder?

Poirot delves back into a crime committed 15 years earlier and discovers that, when there is a distinct lack of physical evidence, it's just as well that "old sins leave long shadows".