When two individuals living with Multiple Personality Disorder cross paths, they initiate a complex psychological investigation into the fractured architecture of their own minds. Penny Driver, known as Mouse, struggles to maintain control over her life as she experiences frequent blackouts and memory loss. She seeks out Andrew Gage, a man who has successfully organized his own internal personalities into a structured, imaginary house. As they collaborate, Andrew realizes that his internal sanctuary contains a hidden, locked room that threatens to dismantle the fragile stability he has fought to maintain. The narrative explores the internal landscape of the human psyche, utilizing a perspective that shifts between the external reality of the characters and the internal dynamics of their multiple identities.

This novel is frequently noted for its imaginative approach to the complexities of dissociative identity disorder, moving beyond clinical tropes to create a distinct internal world. Readers and critics often highlight the technical skill required to maintain the distinct voices of the various personalities residing within the protagonists. The narrative is characterized by its ability to balance psychological depth with the pacing of a suspenseful mystery. The book suggests that the process of healing involves confronting the most guarded aspects of one's own history, a theme that resonates throughout the development of the internal house metaphor.