"A Right to Die" by Rex Stout

This is one of the best fiction books I have read that concerns the Civil Rights Movement and was actually written during the 1960s. 
A father asks Nero Wolfe to investigate his son's fiancee because he is sure there must be something wrong with her or her past, and that his son needs to be aware of it.  The father and son are black, and the fiancee is white, and it's 1964 -- the father is sure that either this girl has ulterior motives for wanting to marry a black man, or she is simply toying wi...