This book has no beginning or end and no fixed protagonist. It has no overarching plan or general plot.
The first four volumes are all mysteries, each a self-contained detective story.
The final volume is a collection of strange supernatural ghost stories. Each tale stands alone, with no continuity between plots, so you can dip in anywhere!
If other people's books are like snakes, where no part can survive on its own, then mine are like earthworms: take any part you like, and it can live by itself. You could call it a rather unusual collection of stories.
[If you like mysteries, read the first four volumes. If you like supernatural tales and ghost stories, read the later ones.]