The discovery of magnetic sleep in 1784 marked the beginning of modern psychological healing. It revealed mental activity that was not available to the conscious mind but could affect concious thought and action. This book tells the story of its discovery and its relationship to psychotherapy.

He documents how the systematic investigation of alternate consciousness reached its height in the 1880s and 1890s, fell into neglect with the appearance of psychoanalysis, and is now experiencing renewed attention as a treatment for multiple personality disorders that may arise from childhood sexual abuse.