Lisette Ashton 
The Black Garter [EPUB ebook] 

Ruthless and beautiful, Hera leads the Black Garter with a merciless hand. Her elite group of prefects secretly patrols the Kilgrimol Finishing School for Young Ladies. They help her to administer cruel and degrading punishments whenever Hera deems it necessary. New recruits are subjected to humiliating initiations, but the treasured prize of acceptance makes it a sacrifice worth enduring.
When a spate of scandals strikes the school, private investigator Jo Valentine is called in to find the souce of these incidents. Finding herself drawn in to a world of perverse pleasures and sexual intrigue, she soon realises that the kilgrimol Finishing School is no place for a lady.