Charlie Bone and the Invisible Boy (The Children of the Red King, Book 3)

This semester at Bloor's Academy brings a few changes. There is a new art teacher, Mr. Boldova, and a new student named Belle, who lives with the Yewbeam aunts and seems to have strange power over them. Emma and Charlie soon discover Mr. Boldova's secret identity: He is the older brother of Ollie Sparks, the boy who lives in the attic of Bloor's Academy. Ollie had always been prying into matters that didn't concern him, so Ezekiel Bloor had made him invisible. When Charlie and his friends find him, Ollie is alone and hungry, so they promise to help him become visible again.