When Cammie Morgan enrolled at the Gallagher Academy for Exceptional Young Women, she knew she was preparing for the dangerous life of a spy. She just didn't know that life would start during her junior year of high school. But that's exactly what happened when Cammie faced off against a mysterious organisation called the Circle of Cavan. Now even Cammie 'The Chemeleon' can't hide. Danger has followed her to London where she discovers one of her most trusted allies has been labelled a double agent. The Gallagher Girls quickly realise that the Circle's agents are closer than they'd feared - maybe even within the Gallagher Academy's own walls. Cammie and her room mates must call upon old friends if they want to find the traitor at their beloved school before it's too late. In this four installment of the New York Times bestselling series, the Gallagher Girls, must hack, spy, steal and lie their way to the truth as they go searching for answers, recognising that the key to Cammie's future may lie deep in the past.