Lady Hampshire thinks that Petofi is behind the music box. They appear to have an interesting backstory.
Yes, as Petofi and Kitty were talking, I was thinking that I would love to see the story acted out. Why did Petofi bring the the Earl down? He wouldn't have done it out of sheer malice; there must have been something in it for Petofi.
Meanwhile, we're seeing how Kitty got herself promoted from governess to countess: by boldness and determination. There was a hint from Petofi that once upon a time, even being a governess was a step up. I'm not sure about that, though. He suggests that her original station in life was pretty awful, but maybe that's how he thinks of being a governess.
I was thinking today that the big difference between Kitty and Rachel was courage, but I changed my mind. Rachel was very brave. But she had no thought of self-advancement. When Rachel learned of Barnabas's engagement to Angelique, she put aside all thought of him. For her, it wasn't about advancement, but about caring. If Kitty had been in Rachel's place, I think she would have continued to pursue Barnabas.
I was surprised to learn that Quentin was familiar with the music box, and that he said it belonged to Barnabas. When last we saw it, Barnabas was giving it to Rachel. Quentin couldn't have seen it before that. Did Rachel give it back to Barnabas on learning that he was engaged to Angelique? Or did Barnabas go and take it from her things after she died? Or did the music box trot back to Barnabas on its own?