Yes, you’re right: the title is a portmanteau. It’s not a concatenation of “dead mistress” but a portmanteau of “dead” plus “headmistress.” Get it?
This 2011 mystery by Carole Shmurak wasn’t so easy to find. CommCat couldn’t locate it for me in Massachusetts, but I was able to get a copy through interlibrary loan from Central Connecticut State University, where author Shmurak is a professor emerita IRL. (Of course you recall my review from eleven years ago of Jo Walton’s wonderful novel, Among Others, a book that has been called “a love letter to…interlibrary loan,” for exactly this sort of reason.)
This is the first of four books in the delightful Susan Lombardi trilogy (I think of them as a trilogy since I’ve only read three of them so far). Deadmistress is easy-to-read, humorous, and engaging. Most importantly, it’s an academic mystery—both college and high-school—so it held my attention for that reason. The high-school end of things takes place in an elite New England prep school, so that was particularly meaningful to me, even though in this case it’s an all-girls school. I’ve never been in an all-girls school, either as a teacher or as a student (what a surprise), but it all rings true to my ears.
SPOILER ALERT: At least in this case the perpetrator isn’t a math teacher, as it is so often in fiction. Surely not in real life, however.