Charlie Bone and the Castle of Mirrors (Children of the Red King, Book 4) by Nimmo, Jenny [Hardcover(2005/7/1)]

Charlie Bone is back at Bloor Academy, where a new semester-and new powers-await him. But nothing is quite the same as Charlie left it. A mysterious student seems to be magnetic. One of the new teachers stands out-for all the wrong reasons. And before long, Charlie learns that his friend Billy has been locked behind a force field in the spooky Passing House.But when Charlie discovers the secret of the Castle of Mirrors everything changes. Sinister forces are at work, and only one of the endowed children can set things right again. But who? ( amazon)