In 1907 Sigmund Freud and Carl Gustav Jung began what promised to be both a momentous collaboration and the deepest friendship of each man's life. Six years later they were bitter antagonists, locked in a savage struggle that was as much personal and emotional as it was theoretical and professional. In between them stood a young woman named Sabina Spielrein, who had been both patient and lover to Jung and colleague and confidante to Freud before going...