The Ghosts of a Housekeeper

The book is about an unnamed governess who takes care of some kids. She starts seeing people specifically two figures a man and a woman. It becomes clear that she is seeing apparitions of the former governess Mrs. Jessel and a man named Peter QuintWho I think worked as a servant. There's also the implication that they might have gotten into some untoward activity with the children. That it might have been some sort of sexual abuse happening or something like that.