Story related, can’t miss. Chapter 6, after “The Ghost of Dread Hill”. A long trek here. First talk to Dr. Linkweller in his office, then use the “Shredded and Restored Newspaper” trick on Harvey in the library using paper from the desk there. Look around Helena’s room in St. Edmund’s Hall, opening the box under bed with a hairpin and looking at programme on table. Use the Ball and Cup trick on the handyman on floor 3 (if done right, you’ll get the “You should make money out of it” achievement) then flip switch on fuse book. Go across to other 3rd floor, go to room 322 and talk to Kelly.
Use the “Disappearing Ink” trick on her, then get said Ink from the magic shop. After using trick, examine both items in desk and the photos and hair dye on the cabinet. Next to Christ Church garden and talk to Charles, then to main Church area and call Charles’ mother. Finally talk to Dr. Styles in his experiment lab, and the achievement will pop after using all the dialogue options.