Only the Good Spy Young, by Ally Carter, Bk 4 in the Gallagher Girls series

In the previous three books in the series Cammie aka Chameleon Morgan has found out how serious being a Gallagher Girl is.  In the beginning it was fun knowing that she was a spy-in-training, sneaking out to meet a townie boy in Book 1 and using their special skills at detection, evasion, invention and deception to learn more about the mysterious boys from Blackthorne Academy in Book 2.  Things took a darker turn in Book 3 when the girls helped to foil a kidnap/assassination plot aimed at the U.S. Vice-Presidential candidate, a series of frightening and life-threatening situations that showed Cammie and her friends MI-6 legacy Bex, code and invention expert Liz and master of protocol and disguise Macey that spying is serious business.

In the latest installment some questions are answered and even more questions arise - how much power does the sinister Circle have?  How much can Cammie trust occasionally sweet, occasionally frustrating, always mysterious Zach?  Is Cammie's father really dead and if so, how much did his best friend and Cammie's favorite teacher know about it?

Fans of the series will enjoy this entry, and with an ending in which Cammie prepares to put her talents as the Chameleon to the test and set out to find out the truth about her father on her own, it sets the stage for what should be an action-packed book 5, with six books anticipated in the series.