This wasn't as much a "Who Dunnit" as it was a "HOW Dunnit". It wasn't hard to determine the culprit, early on. What kept the reader going was the method used, and the motive. Once I locked down the the bad guy, though, I found it hard to continue reading.
Alane keeps you on the edge with each of the chapters in her books! Read the outstanding Christopher Killer first and you will know the characters better and be hooked!!