I’ve been trying to find a book that I read in elementary school for a long time now and haven’t had any luck. I don’t know the author or title of the book, which I know presents a huge problem. What I do know is this:
I read the book around 1982 — I think I was a 3rd grader
The book that I read was a paperback.
The illustrations were black and white drawings, not photos.
The basic story was about two kids, a boy and a girl, that I think were siblings that went to a beach house for the summer. I think the beach house was owned by their grandparents or an older uncle, etc. The kids find out that there is a large diamond hidden somewhere around the property. They find various clues to the location of the diamond throughout the book and eventually discover that the diamond is a rough cut diamond that is tied on to a fishing net. The fishing net is hanging in plain sight above the fireplace in the house and the diamond appears to just be a weight attached to the net.
One illustration I remember near the end of the book was of the fishing net hanging above the fireplace.
Another illustration I remember is of sand dunes near the ocean with a fence and grass
I’m sorry that that isn’t much to go on, but if you could help me out I’d really appreciate it.