The Maidens by Alex Michaelides

Edward Fosca is a murderer. Of this Mariana is certain. But Fosca is untouchable. A handsome and charismatic Greek Tragedy professor at Cambridge University, Fosca is adored by staff and students alike—particularly by the members of a secret society of female students known as The Maidens.

Mariana Andros is a brilliant but troubled group therapist who becomes fixated on The Maidens when one member, a friend of Mariana’s niece Zoe, is found murdered in Cambridge.