I haven't read this one so I'm not sure how smutty the contents are (the difference between our regular entries and the After Dark series being akin to the difference between an R or X rating) but, based on what would now be seen as the politically incorrect front and back cover text, I believe one of the twin taboos is interracial love. Possibly interracial lust. Which seems equally taboo for the time, especially in the South.
The other taboo is anyone's guess I suppose. My guess is they're related somehow? If I ever decide to read this I'll get back to you.
And on that note I am off to enjoy what's left of this Friday night via a late dinner and Noir flick on TCM. As for next week, I still haven't quite figured out how I'm gonna adjust the schedule to fit my schedule but again, when I figure it out I'll get back to you.