The Clue in the Diary

This mystery novel follows Nancy and her friends as they stumble upon a burning mansion and find themselves embroiled in a seemingly unsolvable mystery. The anonymous diary they discover contains indecipherable handwriting and puzzling technical drawings, leading them to question who dropped the diary and whether it's connected to an unscrupulous dealer in patents who has gone missing. As evidence mounts against an innocent man, Nancy takes it upon herself to clear his name and solve the mystery once and for all.