Mystery of the Hidden Brooch was a book I read in elementary school in early to mid 70’s. It was a mystery about a missing brooch. There was an old house with a brick wall or chimney upstairs, possibly covered by wallpaper. One of the bricks was a drawer, where I believe the brooch was found. The mystery was solved by a young girl, possibly other children also. I could be confusing a couple of books.
That sounds a lot like The Diamond in the Window by Jane Langton. Eleanor and Eddy (the two children) live in an old mansion with their Aunt Lily. When they overhear that the house will be taken away and demolished if their aunt can’t raise the money for back taxes, they begin investigating the house. They discover a hidden room in the attic with twin beds and a chest of toys that had once belonged to Aunt Lily’s younger brother and sister, Ned and Nora, who had vanished years ago, along with Prince Krishna. They then find a note from Krishna promising wealth to whoever can follow a trail of clues, so they decide to search for the treasure in order to save the house. I believe the treasure ends up being a ruby brooch.
I think that it’s possible that you could be confusing the plots of multiple books. One of the books might be Key to the Treasure by Peggy Parrish….Which I loved! Three children (2 boys and a girl) go to stay with their grandparents for the summer. There are quite a few clues – including one behind a brick.
This could be the book “The Secret of the Old Sampey Place by Frances Fitzgerald. Judy finds her great-aunt’s onyx and diamond brooch behind a loose brick in the wall.
The Secret of the Old Sampey Place by Frances Fitzpatrick Wright is the book I have been looking to find for 30+ years! Thanks so much for your help. I checked this book out at our local library and as soon as I saw the illustrations, I knew it was the one. It was like finding an old friend!