M G Eberhart [books]
You may not have heard of Mignon Eberhart. I hadn't before I took part in a mystery and thriller-themed knitting swap. (I knitted a Maltese Falcon, which came out more like a Maltese Penguin, for my partner, she sent me a stupendous Poirot-themed tea cosy.) My partner also sent me a book by Mignon Eberhart because I enjoy both Rebecca by Daphne du Maurier and Laura by Vera Caspary.
The two you see here were first printed about two decades apart, The Glass Slipper in 1938 and The Promise of Murder (also printed under the title Melora) in 1959, yet they are similar enough to be a good illustration of Eberhart's most famous style of story. Both feature a beautiful young second wife, married to an older, successful man. In each case there's a beautiful, chic woman closer in age to the husband involved in the couple's lives, usually making the new wife feel gauche and unwanted. I have other books by Eberhart, but the out-of-place central female character and luxurious settings are a constant, and there's always a good dollop of romance to counterbalance the thriller element.
I don't enjoy romances as a rule, but do enjoy a good crime novel, and find these interesting for the precise descriptions of women's lives, and what happens when crime enters the precise, elegant world of rich women. You get a sense of clothes, jewels and good manners working as both armour and prison. Eberhart's stories are quite feminine, a little 'soapy', and that's not a bad thing but I do think they'll be enjoyed more by women than men.
Like a lot of older crime novels, you may find these popping up in your local Oxfam or secondhand book shop, although I don't think they've been reprinted in recent decades.