In 1896, a young Genevan medium named Hélène Smith perceived in trance the following words from a Martian inhabitant: "michma michtmon mimini thouainenm mimatchineg." Those attending her séance dutifully transcribed these words and the event marked the beginning of a series of occult experiences that transported her to the red planet. In her state of trance, Smith came to produce foreign conversations, a new alphabet, and paintings of the Martian surroundings that captured the popular and scientific imagination of Geneva. Alongside her Martian travels, she also retrieved memories of her past lives as a fifteenth-century "Hindoo" princess and as Queen Marie Antoinette.Today, Smith's séances may appear to be nothing more than eccentric practices at the margins of modernity. As author Claudie Massicotte argues, however, the medium came to embody the extreme possibilities of a new form of subjectivity, with her séances becoming important loci for pioneering authors' discoveries in psychology, linguistics, and the arts. Through analyses of archival documents, correspondences, and publications on the medium, Massicotte sheds light on the role of women in the construction of turn-of-the-century psychological discourses, showing how Smith challenged traditional representations of female patients as powerless victims and passive objects of powerful doctors. She shows how the medium became the site of conflicting theories about subjectivity--specifically one's relationship to embodiment, desire, language, art, and madness--while unleashing a radical form of creativity that troubled existing paradigms of modern sciences. Massicotte skillfully retraces the story of this prolific figure and the authors, scientists, and artists she inspired in order to bring to light a forgotten chapter in modern intellectual history.