The Cater Street Hangman started off a little slowly for me, but it picked up fairly quickly. I enjoyed the process of the mystery, even though I had the culprit pegged very early. I liked how Perry got into the heads of her characters, and how she explored their psychology a bit. It was this exploration that made the book engaging.
I did find that the book became clunkier, even rushed, toward the end. It was as though Perry spent all this time breathing life into her characters and making an elaborate story for them to live in, and then she realized, "oh, crap. I've got a mystery to wrap up!" There were a few loose ends that were left loose, and a couple of very important developments that happened at kind of a weird juncture in the story, and the ending was abrupt! In spite of all this (and more), though, I did get swept away by this book. I don't know. Sometimes proper Victorian swells and grisly Victorian murders are just the thing.