Books of Magic (Books of Magic Vol. 3 #16)

Tim's burgeoning magical abilities got onto the radar of the London police, but he was able to keep them at bay... until Detective Celia Culpepper of the Other Side took his case. She's a sorcerer herself-quite a powerful one, it seems-and now there's no place Tim can hide! But should he hide? Or does Celia have much grander plans for Tim than locking him away? He'd better decide what side she's on soon... because Tim's evil doppelga nger is on the loose, and Tim can't stop him on his own!