I found this novel pretty good, a little unexpected, too. The basic events are true, emptying and purifying the Cemetery of Les Innocents as an emergency because it had been so overused. One can find a couple pictures of the church and cemetery on the Internet in Google Images. The protagonist himself is not a real historical character: I looked.
The strange mummified princess that the organist is so interested in was historical, but made of wax, a big street museum thing at the time. The text does not make that clear, and the signs for the attraction probably didn't either! I found it in Schama's history "Citizens," which I think the book is based on.
"Pure" can be read without studying the French Revolution -- it's set in 1785 and the revolution didn't really start till 1789. However, it's full of ominous hints of trouble coming: the graffiti that keeps getting written on the walls of the cemetery that connect the purification the engineer is doing with the perceived need to purify France of the queen and all the king's ministers. The minister laughing at the extreme radicalism of the play "The Marriage of Figaro," and laughing was not the right response, because they tolerated radicalism that would destroy them. The engineer suddenly changing to dressing all in black: that would be a standard costume of the revolution.