This is the story of how a middle-aged spinster lost her mind, deserted her domestic gods in the city, took a furnished house for the summer out of town, and found herself involved in one of those mysterious crimes that keep our newspapers and detective agencies happy and prosperous.
Based on the first sentence, it's ambiguous whether the spinster lost her mind prior to going out of town for the summer or as a result of subsequent events.
From the later paragraphs, it seems to be that the mere act of deserting "town" for the summer like everyone else was deemed a not very sane thing to do by the narrator.
I figured I'd start this even if I didn't end up counting it for booklikes-opoly (I'm still in the middle of The Grass Grown and I plan to finish it) so that I can tag along for the buddy read. Some clarification of the new free Friday rules would be nice, however.