We've reached the trial and things have really gotten interesting.
Two points though:
1) While he does a decent job of putting the story into a larger context, if you don't know very much about this time period in French history, some of it might fly over your head. I'm glad I waited to read this till after reading Dawn of the Belle Epoque. Twilight of BE deals with the new century (1900), so it's not necessary. Other books might do just as well, but the extra info definitely helps.
2) The author writes this book with an American voice. Not necessarily a bad thing, but also something I'd not really notice in most cases but did here. Just something I've seen the last couple of pages and I'm mulling over.
Did a search on him and found an article he wrote about the Eiffel Tower, which corresponds to the time period of this book. He mentions some things that come up in the book as well. If you are interested in the book, you might wan to take a glance at this. Article by the author.