Charlie Bone and the Invisible Boy by Jenny Nimmo

Charlie and his friends learn that a boy is hidden in the school, Ollie Sparks and become determined to sneak him out of Bloor's. The only catch is that he's invisible thanks to a magical boa. His older brother has come to the school as an art teacher in search for him. To make matters worse, a beautiful but suspicious young girl named Belle shows up at school, quickly siding with Manfred and his lackies (Asa, Dorcas and Zelda). And a sorcerer named Skarpo is on the loose and Charlie is to blame.
When it comes to character development, Billy finally admits to what Ezekial Bloor made him do, and decides to no longer be a spy. He and Charlie become friends again, a happy occurrence.
Benjamin Brown takes a holiday from this book (literally), going to Hong Kong with his family. I'm not sure about the author's decision behind this. Maybe this way we can focus on the other characters, after all, there are many.
Belle is creepy new character that we don't know what to think of. She is obviously more than she seems.
Charlie's character development is limited to him making a big mistake when he goes into a painting. Peton soundly scolds him but we're not sure he has learned anything from it.
To see how it ends up with the missing sorcerer, is surprising to say the least. It ends up playing a small role, which confused me. But considering how most of the book is preoccupied with Ollie Sparks, Skarpo simply serves as a way for Charlie to get his new wand. I wasn't sure if I liked this at first but on second thought, he did serve a purpose.
The most dramatic of scenes is when Charlie and his friends head to the Yewbeam Aunts' house to steal a plant that will heal Peton. That and when the aunts' attempt to kill Julia Ingledew (Emma's aunt and Peton's love interest) and Peton confronts them. That's probably one of the most rewarding scenes in the book.
For another story of adventure, creepy villains, and determined heroes, I give "Charlie Bone and the Invisible Boy" four out of five stars.
If you want to learn more about the author, check out her website.