The Clue in the Diary (Nancy Drew Series #7)

Nancy and her friends, George and Bess, are returning from a country carnival when they witness the explosion and burning of a beautiful country mansion. Fearing its occupants may be trapped in the blazing building, they rush to the rescue - and unexpectedly fund themselves confronted with a mystery that seems to be insoluble. The first clue, an anonymous diary, includes not only indecipherable handwriting, but puzzling technical drawings and chemical formulas as well. Who dropped the diary...