Strong Poison is the start of the Peter/Harriet arc, so that can indeed be a good place to start. Nine Tailors I read ages ago, but I remember it as atmospheric and lovely. Looking forward to rereading it when the podcast gets to that point!

For now I've pulled Strong Poison and Have His Carcase off the shelf for you; if you like them enough to want to read the series, you can fill in before and around... I'm also still in the middle of writing up all my many recs for you, but I'll email you soon & we can arrange pick-up. :-)