This is the story of Timothy Wilde, a former bartender who comes to serve on the brand-new NYPD, and his efforts to solve the apparent murders of several child prostitutes. Along the way, Faye weaves in public health issues of the day (set in 1845), prejudice against Irish immigrants to NYC, commentary on religious strife, and class tensions. I enjoyed it very much.
Soapbox time: I'm half Irish Catholic and half English, and I'm old enough to remember when Catholics were commonly called "Papists" (as a slur). My WASP grandfather refused to attend the wedding of his son to my Irish Catholic mother, is what I'm saying--this prejudice isn't as long-gone as you might think. I even find it comes up from time to time here in the present-day South (where I live now). So it was refreshing to read about it, given that many people think, "Oh, it wasn't that bad for them." Yes, it was. /soapbox
Anyway. This book rang true to me in all historical aspects, so brava to Faye. I especially liked the way she wove in the patois of the underclass ("flash"), from which we get some of our present-day slang (e.g., pal, cop). Very interesting. I also cared about the characters, and didn't guess "who dunnit" because of a couple of nice twists toward the end. A solid read.
EDIT: I just found out she's got another Timothy Wilde book out now, Seven for a Secret.