I read a series of kids books while I was in elementary school for class and we never finished the series. I remember it was about a group of teens and one them just moved in and finds hidden passage ways underneath his house. He learns it's linked to pirates and it they lead to treasure if navigated corrected. I want to say that captain kid was the person behind the treasure being hidden. Another random detail is the kid with the passage ways under his house is crazy attentive to time because his dad is never late and when he says he will be home, he is always home at that time. I can't remember how many book store were in the series but I know it was more than four.