Showing Cross My Heart and Hope to Spy by Ally Carter

There I was: Cammie the Chameleon--the Gallagher Girl who had risked the most sacred sisterhood in the history of espionage. For a boy. But I was through with lying. And sneaking around. I was going to be...myself.

Despite Cammie's best intentions to be a normal student, danger seems to follow her. Cammie and her friends must clear her name by discovering the truth about some mysterious guests...but this time the stakes for Cammie's heart - and her beloved school - are even higher.