Request #137

I don’t have much to go on. A kid/YA book that I checked out from my grade school’s library. Between 87-92. I remember reading it in earlier years, and I read it more than once. It was about a young girl who was solving some kind of mystery. Not sure if it was a game or a real mystery. And she was cracking some kind of a code in an old house. Like on a lock or safe or something. And the book showed dashed lines for the code like _ _ _ _ etc. And every time she found a letter, the book filled in the letters. ____S____E___
The code ends up being Chrysanthemum. And it’s IMPOSSIBLE to search for this because there is a book called Chrysanthemum.