The Bird's Nest: Shirley Jackson

The protagonist, Elizabeth Richmond is introduced as a very plane woman who has more and more time she can't account for or remember as the book progresses. She is soon diagnosed with multiple personality disorder as 4 distinct personalities emerge. we find out her mother had had a personality illness and Aunt Morgan, who has raised her since her mother's death, is about at wits end dealing with the "four" women. Elizabeth's personalities seem to have "spilt" from the death of her mother, which is seems like she had a part in when Elizabeth shook her mother. her mother was seeing "Robin" who didn't want a child and Lizzie can't remember if her mother ever defended her. Aunt Morgan and Dr Wright get Lizzie to understand that her mother is dead, because one of the personalities, Betsy, believes she is still alive and Beth, thinks her mother just died 3 weeks ago. Once the girls come to the realization their mother is dead, they all merge back into the one personality, or so we believe.