The Dead of Winter by Rennie Airth

A young Polish immigrant is murdered in blitz riddled London.  The fact that she was working for retired detective John Madden who has left  London to be a gentleman farmer in the countryside draws him into the mystery.  As the bodies pile up, the solution seems to cross decades and continents.  This is great period history as well as mystery and Madden is as much the insightful, gentlman detective in this book as he is the first two mysteries in this series.