Out of Sight, Out of Time, by Ally Carter (Gallagher Girls book #5).
It wasn't like we talked a lot. But then again, it's not like there was all that much left to say. We'd seen things. We'd done things. And I wasn't the only one who was still waiting for me to come home from my summer vacation.
I leaned over the sink and let Bex wash and bleach my hair. Then Macey took the scissors and trimmed away my dead, uneven ends. I sat, letting my best friends work around me, watching as the person I had been last summer washed away down the drain.
She calls her mother (who is also the headmistress of the school) and is brought back to the Academy, where her friends have been worried sick about her. Cammie must figure out what exactly she did over the summer, and how she ended up at the convent in Austria.
This book was so good that I read it in about two hours. Seriously. My only regret is that now I will have to wait a while for the next installment; as in all of her Gallagher Girls books, Ally Carter gives us an ending that foreshadows the next book. I will caution you that this is not really a "stand alone" book, at least if you want to understand the nuances of all of the relationships going on - definitely read the first four books before reading this one - but even if you had not read any of the other ones, the spy stuff in it alone is enough to keep a reader interested.
5 stars out of 5.
*Disclosure: I was a given a copy of this book to review. The opinions listed, however, are my own.
And the "trailer" for the novel is pretty awesome as well: