Sybil Dorsett, a pseudonym for psychiatric patient Shirley Mason, is the protagonist of this book, and her struggle with her multiple personality disorder is the entire subject of the book. By the time Sybil first becomes Dr. Wilbur’s patient at the age of 22, she has already been suffering for most of her life from what she elliptically calls “lost time.” At the beginning of the arc of development this book traces, Sybil is only a waking self, a “depleted self,” because childhood abuse has driven her to siphon off so many of her original traits into her other personalities (455). These other personalities, Dr. Wilbur ultimately determines, were born within her to take over consciousness when reality was too unbearable for Sybil to live through. Because there was no escape from her abusive home, Sybil’s alternate personalities swooped in to live much of it, allowing her to escape psychically, if not actually.

Sybil has sixteen personalities, who all vehemently feel themselves to be independent people. But the contrast and conflicts between them are represented by the two most important personalities, Peggy Lou Baldwin and Victoria Antoinette Scharleau. Peggy Lou is a wild, child-like personality, an expression of Sybil’s primal feelings of rage and anger.