This is a historical novel that is an imaginary riff on a historical mystery. Denis Diderot (the primary editor of the Encyclopedia that more or less let the rulers of the Church and State in France know that the Enlightenment was here to stay) had some kind of relationship with a woman named Sophie Volland. History doesn't know who she was or what was the nature of their relationship. Prange uses his imagination.
He posits that Sophie is a provincial village girl, raised in poverty but taught to read by her free-thinking mother who was the last witch to be burned in the village. Sophie goes to Paris to try to find the man who perjured himself and testified against her mother. In Paris, she meets and falls in love with Diderot, who is already encumbered by both a wife and a mistress. She also meets and becomes friends with the Marquise de la Pompadour, the mistress of the King and arguably the most powerful woman in France. Sophie is both a witness and a participant in the run-up to the French Revolution.
It could be read as a simple story of love, loss and betrayal. And there's plenty of all of that. It is also a story about people who believe so passionately that ideas are important and that new ideas and new ways of thinking must not be impeded by old-school thinking, prejudice or fear. The philosophes as depicted by Prange are deeply flawed people whose passion for what amounted to a fundamental shift in the way educated people viewed reality allows them to challenge both Church and State without regard for what that might mean for them. They were bound together by their commitment to publish the Encyclopedia, regardless of the personal costs.
One thing annoyed me enough to make a note of it. I don't know if it's was the fault of the author or the translator. The author calls Paris a "kraken" at least a half dozen times in the book. I got it the first time. The second time emphasized the point. After that, it became annoying. (I am sorry if that's a trivial criticism. I don't think I've ever had one word pop out and annoy me so when reading a book. Maybe it struck me because kraken is an unusual word in English. Perhaps its repetition would not have stood out so starkly in the original German.)
I give this one a pretty solid thumbs up, especially for readers who are into French history. It certainly paints a rich and complex canvas of pre-revolutionary France.