The A.B.C. Murders by Agatha Christie

Alice Asher of Andover has been murdered. It seems to be an open-and-shut case of a woman killed by her brute of an ex-husband. So why is Hercule Poirot interested? Well, he received an anonymous letter about the murder. And when Elizabeth "Betty" Bernard is murdered in Bexhill, the stakes are definitely raised.
Poirot gathers some of the people affected by the murders, especially when the victim of 'C' turns out to be a well-known gentleman. It is in talking to these people that Poirot discovers the insidious reason for this series of murders.

Hercule Poirot #13

Four stars

This book came out January 6, 1936

Follows Death in the Clouds 

Followed by Murder in Mesopotamia

Borrowed as audiobook from Hoopla

Opinions are my own