Nancy is not investigating the Ku Klux Klan, instead it is a "nature cult" that is renting outlying property attached to the struggling Red Gate Farm. Cover confusion aside, this was a pretty solid book and, even though one of our villains is half-Chinese, there isn't any reflexive racism. Progress??! I think so.
On a shopping trip Nancy, George and Bess are looking for a new perfume and think they've found it in an import shop near the train station. With reluctance, the shop girl sells them a bottle for the exorbitant price of $3! Wearing the scent, Nancy is approached by a mysterious man and mistaken for a message-bearer. What is going on? Meanwhile, the girls have befriended a timid girl named Millie who is seeking a job in the city to help support her grandmother and save the family farm which they were forced to mortgage.
Circumstances lead Nancy and friends to become paying boarders at Red Gate Farm to help Millie and her grandmother and, of course, get involved in a mystery surrounding the "Black Snake Colony", a peculiar cult whose members are sometimes seen dancing around on the hilltops at night.
Changes to this text appear to be minimal, but I never read this one growing up so I can't say for certain as I'm going by other's comment. There was a name change to Millie, a snakebite, and some minor plot and character shuffling to get with the modern 60s times.
I am surprised there were no changes made to style of the robes the cult uses. It is a plot point that the robes had to be distinctive and stand out on moonlit nights, so perhaps the editors couldn't think of an alternative to pointy hoods and white sheets.
I'll be taking a break from Nancy until I get my hands on book seven.
Nancy Drew Mysteries
Next: 'The Clue in the Diary'
Previous: 'The Secret at Shadow Ranch'