What if a world-renowned philosopher and professor of psychiatry at Harvard suddenly announced he believed in ghosts? At the close of the nineteenth century, the illustrious William James led a determined scientific investigation into "unexplainable" incidences of clairvoyance and ghostly visitations. James and a small group of eminent scientists staked their reputations, their careers, even their sanity on one of the most extraordinary quests ever undertaken: to empirically prove the existence of ghosts, spirits, and psychic phenomena. What they pursued—and what they found—raises questions as fascinating today as they were then.