I confess to reading Jean Plaidy during my teenage years, my interest fired up by a nun teaching us history, who uttered a bizarre pronouncement on a specific book by that author, kind of advocating it on the one hand, but with the caveat "it will give you some knowledge of that particular period, but don't read between the pages of whatever and whatever, because even married people don't do that"
To us at 15 that sounded irresistible! naturally we all acquired the book if only to access those pages. We concluded she'd got that book mixed up with something else, that maybe she'd been reading covertly "The Tropic of Cancer" or "Lady Chatterly" possibly!!! I guess she knew what she had in mind, but as far as I could see, it wasn't in a Jean Plaidy, I read quite a few after that.