I dropped this book around page 100; it was just too fluffy, while at the same time annoying.
I don't think the things I didn't like will bother every reader. My chief gripe, a common with historical fiction, is that it was just too inaccurate. The way the characters thought, the ways they interacted, their public behavior, these were just not correct for the Regency period. But obviously for people who don't know or care much about history this won't matter. It's just a deal breaker for me because every other line I am all "Nooo, he/she would never say/do that!" and it totally takes me out of the story.
My other complaint is that I felt like the plot etc was really obvious, partly because the elements are so heavily telegraphed and partly because -- well, I've read this story before. This is basically some Elizabeth Peters mummy color tossed into a YA rewrite of the Pink Carnation series. Only even fluffier, and that's really saying something because Lauren Willig is pretty damn fluffy already. But she does better research, and has stronger characters. Like a lot of YA historical heroines Agnes didn't seem to have much to her aside from her anachronistic spunk.
But I don't want to slam the book. I could see a girl in her early teens who hadn't read a lot of this sort of story before really enjoying it. But if you are that girl, message me and I will recommend some similar-but-better books for you to read in a year or two.