What is the theme in Major Pettigrew's Last Stand: A Novel by Helen Simonson?

Proper behavior is the main theme of the story. Major Ernest Pettigrew is a retired Major from the Royal Sussex. The Pettigrew family has a long and illustrious reputation as a proper British family, prone to act in the most proper and ethical manner at all times. Major Pettigrew regrets that modern times have eroded this type of behavior.