The title comes from the British practice by women to give men who were not enlisted in the armed forces a feather as a symbol of the man's supposed cowardice. Many women believed that they really were helping their country by giving the army more men. And of course, plenty of them had little idea of the utter massacre that was taking place in the trenches at the Front in France.
We learn a bit more about her assistant, Billy--the veteran sapper-- in this novel, and the character development will definitely keep fans of the series on the hook. However, the mystery itself is a tad slow and plodding. This series seems to be developing into one in which the character development is as much an impetus to keep buying the next book as the mystery itself.