The listing, Key To The Treasure by Peggy Parish has ended.
I loved this book as a child. I read it over and over and kept hoping I'd stumble upon a similar mystery in my house to solve. Now, I'm reading the whole series of Liza, Jed and Bill mysteries to my 7 year old twin boys, and they love them as much as I did. It's a lot of fun to share them as a family, a chapter a night. I'd recommend this book (the best in the series in my opinion) as a great gift, even for a reluctant reader. Kids just have to keep turning the pages to see what happens.