Nikki the Invisible Girl (Unabridged‪)‬

When Nikki crosses her fingers, she becomes invisible. Now, she can spy on boys, get even with those school snobs, and even fight crime. But being an invisible crime-fighting middle-schooler has a few complications.
Nikki has three adventures. In Nikki's Birthday Wish, Nikki learns the thrill and responsibility that come with being an invisible pre-teen. In Nikki and the Missing Jewels, our invisible heroine solves the mystery of missing jewels and finds the wisdom to deal with a disturbing truth. In Nikki and the Halloween Ghost, Nikki learns a lesson about transparent friendships.