Recently in looking something up I came across a gentleman by the name of Bill Peschel who publishes some annotated versions of golden age mysteries. The two which caught my eye are The Mysterious Affair At Styles and Whose Body?
I don’t have the time to read them at present, but I’ve put them on my wishlist.
Some of the questions he promises to answer about The Mysterious Affair At Styles are:
Why Would People Drink Strychnine For Their Health?
What Does ‘English Beef and Brawn’ Mean?
What Are Land Smocks? Spill Vases? Patience Cards?
Not having read these I can’t testify as to their quality, of course, but they certainly seem interesting.