Without giving too much away (it's a rather good series, and the reveal is pretty well done), it also might have to do with the book Sybil about Shirley Mason

Without giving too much away (it's a rather good series, and the reveal is pretty well done), it also might have to do with the book Sybil about Shirley Mason https://en.wikipedia.org/wiki/Sybil_(book) https://en.wikipedia.org/wiki/Sybil_(book) https://en.wikipedia.org/wiki/Shirley_Ardell_Mason https://en.wikipedia.org/wiki/Shirley_Ardell_Mason