Henry James 
The Turn of the Screw 

The young governess is hired by a man who has become responsible for his young nephew and niece, Miles and Flora, after the deaths of their parents. He is not interested in raising them and he gives the governess full charge of the children. Soon thereafter, around the grounds of the estate, the governess begins to see the figures of a man and woman whom she does not recognise. These figures come and go at will without ever being seen or challenged by other members of the household, and they seem to the governess to be supernatural. She learns from Mrs. Grose that the governess’ predecessor, Miss Jessel, and another employee, Peter Quint, had had a sexual relationship. Before their deaths, Jessel and Quint spent much of their time with Flora and Miles, and this fact has grim significance for the current governess when she becomes convinced that the two children are secretly aware of the ghosts’ presence.