Funny thing about this book, I actually started reading the second book in the series first, I'll talk about that one in just a few days, but I decided that it would be smart to read them in order, so I got this one from the library really quick and stopped reading the other book. Desi is just a normal, everyday girl. She will be going into the 8th grade soon, she has a job at the pet shop at the mall, and she has some ex-best friends that are now enemies. She's working at the pet shop one day, dressed in a great big gopher head, when she sees her crush Hayden flirting with her ex-best friend Celeste. This is terrible enough, but then Hayden and Celeste come over to where she is standing and Celeste figures out that it's Desi under the head and unmasks her in a most embarrassing way. Desi's not sure why, but she seems to be invisible, almost like...vapor. She is pretty depressed and not sure what to do, so she makes a wish on some fish and the next thing she knows there's someone popping out of a bubble in her bathroom. The someone says that her name is Meredith and that she has Magic Potential, which basically means that she can become any princess that wants to have a substitute. But when Desi seems to mess up her first few cases, she wonders if Subbing is really for her. I really enjoyed this book, it's such a fun story, not to mention that I'm sure most of us have felt like Desi does, invisible vapor. And who doesn't want to see someone come out of a bubble and become a princess, even if only for a little while??!