Showing Miss Zukas and the Island Murders by Jo Dereske

When an anonymous note reminds her of her vow to bring her high school classmates together for a twenty-year reunion, Miss Helma Zukas begins organizing the perfect celebration. When a secret saboteur strands Helma and her old classmates on a fogbound island with a murderer in their midst, the intrepid librarian-sleuth takes charge, with a dubious assist from her raffish friend Ruth.