I am trying to remember the name of a book I read in 5th grade (mid-eighties). It's about 2 boys, one is named Gary, that get caught up in a mystery of some sort and it ends in a cave where they discover the bad guy is the sheriff (or some police official).
I know that's not a lot of information, but if anyone happens to remember it and
Can tell me the title I would be so grateful.

Thank you!