Aside from the creepy mystery, there are some really interesting middle school dynamics going on. While Nate is easily blamed for mischief because he's always in the middle of one scheme or another, it's far creepier to realize that Ainsley, the go-to girl for all events in the middle school, might be the one mysteriously creating trouble! No one will suspect the good girl, who will be given unprecedented access to the school, and unwarranted trust by her classmates! So much more havoc can be wreaked by such a person!
The Library itself is an intriguing space, and there is a lot left undiscovered about its secrets, although we do find out that they still use paper circulation cards. It's nice that Marcus is able to go to Everett for help; as scary as this series is, it's a good idea to have some adult back up just in case. I was very amused by Marcus' choice of extra curricular activity at the end of the book as well.
While there isn't as much about Marcus' biological parents in this book, the ending hints that the trio will investigate the disappearance of Lu's cousin next, and I'm hoping that we find out a little more backstory about both Marcus' family as well as the stories held by the library. We'll certainly have the idea reinforced that having a mechanical fortune teller tell you future is never a good idea! Readers who like MacHale's Morpheus Road series, as well as books by Hahn, Kehret, Poblocki and Barbara Brooks Wallace will scare themselves silly reading The Library with a flashlight under the covers.