Seriously one of the most entertaining books I've read this year. It was a lot of fun trying to figure out the mystery as it went along, theorizing conclusions and revising. In the end, I wasn't suprised, but I was satisfied. The story came full circle with all the ends neatly tucked in. Excellent use of foreshadowing made for compelling anticipation. The relationships were simple, though each one made a point.
This would be an excellent read for a seventh or eighth grade class. It could be used to demonstrate dramatic elements, emphasize attention to detail, and even show cross-class interactions. I can't see anything really objectionable; this would be an easy sell with parents and a good motivator for young readers.