Very interesting approach to mystery/crime solving: Nancy knows almost right from the beginning who the bad guy is, she just has to figure out how to prove it. However, I'm not sure if it's that I've never been all that big a fan of mysteries anyway, or something else, but I found this approach made the story much more tedious. Nancy has MUCH more patience than I do to keep searching for this secret passageway--I was ready to give up a long time before she found it. :P
It was also interesting having the two cases intertwined the way they were. That was very fun to read.
I'm excited to recommend this to my students and to get to see what their perspective on this different approach to a mystery story is.