Request #75

 I’m looking for a book that I read in the late 80s or early 90s, which I *think* was pretty contemporary.

It was one of a series of books about a group of teens or young adults who solved mysteries. The one bit I remember clearly is that they found an old house with a river landing stage, and an old lady who lived there by herself. At one point, one of the girls finds and tries on a dress that they have seen in an old photograph…something to do with the old lady’s lost first love.
It’s possible that they solve the mystery of why her lover went away? I sold the book shortly after, and I’ve always regretted it.