To sum up the story, Madam is like if The Secret History and The Stepford Wives had a love child. Rose arrives in the gothic Caldonbrae Hall as the institute's first new hire in over a decade and finds herself struggling to fit in. As time passes by, she realizes that Hope (as the school is called) is a far more sinister place than she could have ever imagined.
As someone who is interested in the Dark Academia genre, I was excited to read this and thankfully I was not disappointed. Wynne's writing is very atmospheric, and the book has a very chilling tone to it, which is appropriate because the contents are just that. 
It's difficult to write a review for this book without giving spoilers, so all I'll say is that it's definitely one people who enjoy the dark academia genre should read