Also hailing from New York City, Susannah is an African-American (although owing to the fact that she is from a New York of 1964, she prefers the term, "Negro" [see top of article where it states that Negro was preferred prior to the 1970s] over the appropriate term of Eddie's when, "Black") woman with two major afflictions: her legs below the knees were severed in a subway accident (although not really an accident), and a childhood head injury (again, not really an accident) left her with Dissociative identity disorder. She is "The Lady of Shadows", the second companion predicted by Walter to be drawn through to Roland's world via the mysterious doors.

Initially, her dominant personality is that of Odetta Susannah Holmes, a sweet, well-mannered woman active in the civil rights movement. At times, however, she is taken over by Detta Susannah Walker, a murderously psychotic but incredibly crafty and strong willed woman whom neither Eddie nor Roland can control. After an incident at the beach with the lobstrosities, where Roland forces her two selves to see each other for the first time, her personalities are melded into one, and she becomes Susannah (later Susannah Dean, wife of Eddie).

During the drawing of Jake, she seduces the demon of the doorway in order to distract it and afterwards, she falls partially pregnant. Susannah shares the experience of her pregnancy with a demon-turned-mortal named Mia, resulting in Susannah housing another personality in her mind. Mia takes over Susannah's body (and melds with it, giving her legs for a short while), to NYC circa 1999 to help give birth to the demon child.

Susannah is the last of the Humans of his ka-tet to leave Roland (and the only one to survive in a Keystone world), having been given the chance to return to another form of Eddie and Jake in a parallel world.