Harriet The Spy, Double Agent Harriet The Spy Series, Book 5.

Harriet is impressed to learn that the girl she has befriended, now called Annie Smith, is the person who not only created three names-Rosarita Sauvage, Yolanda Montezuma, and Zoe Carpaccio-but also three distinct personalities to match. This girl has potential. Being a spy has always been rather solitary, so Harriet is glad to have a new friend and spy partner. But then Harriet realizes that Annie reveals very little about herself, and indeed, i...