I think the first two books built up to this one nicely. While there wasn't an over all story arc in the first two, it has built up the spy world and characters to make this story arc a very interesting one. In truth, I'm pretty excited for this because while before the stories were fun, I'm hoping things get a lot more complicated as Cammie works to figure everything out.
Things really start to change in this one and it had me on the edge of my seat through most of the book. There is now an unknown enemy out for one of the Gallagher Girls and Cammie doesn't know why. I loved following along as Cammie tried to hunt for the answers and getting more questions in the process.
I think that from this book on things will get very interesting. If you haven't read the first book, do so now! This series is really starting to heat up!