Cool concept for a series. This is the first book I read in the series, but enough background information is given, allowing it to be read as a stand alone.
This is kind of similar to The Magic Tree house books, but with more action and less focus on education.
The plot was good (although a bit unbelievable nine-year-old saving a grown woman is a bit insulting, special agent or not).
The writing was very simple and easy to understand.
In the beginning of the book, there is information given on characters, gadgets, and the GPF, which was helpful for someone who has not read the previous books. However, the first few chapters reiterated a lot of this information, which came off as a little repetitive. I think that the book would have been fine with one or the other, but having both made the beginning a little dull.
Overall, a good read with lots of adventure.