Charlie Bone and the Invisible Boy (The Children of the Red King, Book 3)
This is the third book in the Charlie Bone series. Again, this book is just as good and appropriate as the others and I highly recommend it. In this book, Charlie discovers that a boy has been turned invisible and kept locked away in the Academies attic. Charlie and his friends must find a way to help this boy and prevent the Bloors from continuing their plans.