We are set on Long Island in the early 50s, back when the place was transitioning from mostly farmland into quintessential suburbia. One thing that people may not know about the Island is its history with Nazism, which is the main factor in this book. There were multiple towns that boasted chapters of the German-American Bund, which in the years just before the war were pro-Hitler, would parade down streets wearing Nazi regalia, and even having summer camps along the lines of the Hitler Youth. Yaphank, which in WWI was a training site for American troops, had regular trains transporting hundreds of people for rallies. In this case, we are in Lindenhurst, home to a large community of German emigres who came to the US after the Great War who still thought of themselves as Germans first. Very Nazi sympathetic. After WWII such sympathies had to go underground, but the basic hate in many people's hearts remained, including believers in eugenics, which preached the purposeful culling of all people who were "deficient". It is this theme that drives the story.
Don't be put off reading this book by the above precis. After all it is just a mystery, but with genuine historical precepts, including an unexpected slant on the Lindbergh Baby kidnapping.