Hmmm... Here I am attempting to catch up, since I haven't posted in a month. Let's see if I can even remember what I'd planned to say about this book! I enjoyed it, but obviously you'd need to have read the entire series to appreciate it. It gives all sorts of fun little details and extra inside secrets to the 39 clues world. Definitely for fans, but probably what I'd consider a non-essential. It did set up the next series a bit, which I will plan on reading, but probably not buying (too many books to buy!).