This is the 4th book in the series (which I did not realize at first) but it was very easy to jump right into. I love a good spy adventure novel and this one was so great. Lots of drama and harrowing stunts and narrow escapes, plus clues and a heist and a treasure hunt. I looooved Charlie who may be a genius but is also so fun and sassy and down to Earth, and totally comfortable with all the grownup around her.

I feel like at the age of 34 I learned so much in this book and I love how middle grade books can always teach you fascinating things that are easily digestible for any age!

The audiobook was perfect and I highly recommend this series for all middle grade book lovers!