Superb!

lovely. truly. And what a delicious ending. I love the hint of darkness in your works. They make me smile. A wicked smile, true... but a smile none the less

You write really beautiful descriptions. I think those are SO important for a historical novel to be successful because you have to establish the perfect atmosphere, including time and place to a tee. I found a typo in the first sentence of the "Foiled" chapter. Some of the language is a bit modern, but it doesn't severely hurt the story. The scene at the end of chapter Four was very sensual without being something from a bodice-ripper. Nice job. I hope you post more soon. *faery tragedy

Is that the end then? (Ha, is that blunt enough for you?)

I like the connection of her earlier dance partner and the rival's second. Very interesting.

This was a great conclusion (if it was) and the only comment I have to make is what I feel is the lack of substance.

Okay, so he is fighting a duel to defend her honor, but why is he truly risking his life? Does he have jealousy of Raul etc.?
Also, what are Celine's feelings on the duel and those involved? She seems to be fading in the background, simply sighing and saying "oh no". Is she truly horrified, scared, repulsed?

If you don't understand what I'm trying to get across, I'm sorry.
I'm not sure if any of my comments are going to be that helpful, but I tried my best in the current state of school-frazzeled brain I am in.

Overall, this was a well written story and I enjoyed it quite well! :)

I find the fake count's dialogue rather creepy in this chapter. However, it definitely fits the mood...

Celine's character is very unclear at this point. At first I thought she did not want the intentions of the fake duke, and then suddenly she seemed very pleased with being "ravished" by him.

On second thought though, does she accept his intentions at first because she thinks he is the real count?

Anyway, very good chapter, and you keep the element of suspense by your last sentence. Bravo! :)

"An embony hand shot out..."
Do you mean ebony?

"No. I've not even scene Vermillierre."
I'm sure you mean "seen"

"You're not danced with the soprano?"
"You've" perhaps.

The element of suspense you build in this chapter is excellent. Who was the masked man who went off with Celine?

You have very clear conversation, and you show the nature of some of the characters.

Sorry that most of my comments were grammatical corrections, there was not much more to "pick-apart" in this chapter!

Your second chapter is very good. It includes very witty banter and beautiful descriptions.
The only fault I find is perhaps some over-describing. In the second to last paragraph, the descriptions become very overwhelming, and I felt claustrophobic with all the colors, objects and noises.
Although this could have been a technique you were trying to impose on the reader, I found it could have been less flowerly so I could have atleast formed a slight picture of it.
As it was, my head was filled with a jumble of senses, feelings and sights that made absolutely no sense.
So I reccomend cutting down a little bit so that a reader can differentiate between a person and a tapestry.
However, don't feel the need to if you wished to create a blur of images which is sometimes intended.

I love love the conversation in this chapter. (love love...quite improper).

Here is my "picking apart," and I'm terribly sorry if you find any of my comments unuseful. I will try my best!
(I am doing it by chapter just so I don't have a horrificly long review at the end. Also, I may not be reviewing all the chapters at once anyway.)

"Did you hear her sing?" Francois, his friend, returned."
It doesn't make much sense that he would be asking his friend if he had heard her sing, if they had just attended an opera together, which consists of singing..

This is really trivial and my own personal opinion, but where you say:
"...we'd have to duel for the favor of your gaze," Léontin joked." the word "joked" seems a bit out of place with the language you are using, so I would reccomend using "teased" or "jested" instead.

Another thing is that some of your introductions of characters are more confusing than vague. For example, in the beginning, when you mention Andrea's sister, I was confused as to who she was. "Is she Celine? If not then where/who is she?"
Something that could solve that would be being more clear about the characters without explaining them too much, as I'm sure you'd prefer it.