When I was in middle school my dad came home with one of the many Three Investigator books. He had been telling my brother and me about them for weeks and finally found some at a Half Priced Books. My brother and I loved mysteries and dad read all the Three Investigator books when he was a kid. Soon enough dad was stopping at yard sales and book stores looking for a bargain so we could read them all. Years later I still love all of these books. They are a fast read but the mood the books put you in as you read them is priceless. I don't remember what happened to all those books we acquired, but we don't have a single one anymore. I am now on a mission to find them all to keep.
If you have a child that doesn't like to read or one that loves to read, these books are perfect. My younger brother is Autistic and we always tried to find books for him to understand and enjoy. At 20, these books are still his favorite and are the ones that started his love of reading.
I love reading about the three teenagers, one has the brains, one the common sense and one is the aggressive. Each boy has a important role in solving the mysteries. I enjoy these books better than the Hardy Boys.