The Turn of the Screw by Henry James

An unnamed narrator listens to a male friend reading a manuscript written by a former governess whom the latter claims to have known and who is now dead. The manuscript tells the story of how the young governess is hired by a man who has found himself responsible for his niece and nephew after the death of their parents. He lives in London and has no interest in raising the children. The boy, Miles, is attending a boarding school whilst his sister, Flora, is living at the country home in Essex. She is currently being cared for by the housekeeper, Mrs. Grose. The governess's new employer gives her full charge of the children and explicitly states that she is not to bother him with communications of any sort. The governess travels to her new employer's country house and begins her duties.
Miles soon returns from school for the summer just after a letter from the headmaster stating that he has been expelled. Miles never speaks of the matter, and the governess is hesitant to raise the issue. She fears that there is some horrid secret behind the expulsion, but is too charmed by the adorable young boy to want to press the issue. Shortly thereafter, the governess begins to see around the grounds of the estate the figures of a man and woman whom she does not recognize. 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 her predecessor, Miss Jessel, and Miss Jessel's illicit lover Peter Quint both died under curious circumstances. Prior to their death, they spent most of their time with Flora and Miles, and this fact takes on grim significance for the governess when she becomes convinced that the two children are secretly aware of the presence of the ghosts.