In 1953, a twenty-seven-year-old factory worker named Henry Molaison—who suffered from severe epilepsy—received a radical new version of the then-common lobotomy, targeting the most mysterious structures in the brain. The operation failed to eliminate Henry’s seizures, but it did have an unintended effect: Henry was left profoundly amnesic, unable to create long-term memories. Over the next sixty years, Patient H.M., as Henry was known, became the most studied individual in the history of neuroscience, a human guinea pig who would teach us much of what we know about memory today. Patient H.M. is, at times, a deeply personal journey. Dittrich’s grandfather was the brilliant, morally complex surgeon who operated on Molaison—and thousands of other patients. The author’s investigation into the dark roots of modern memory science ultimately forces him to confront unsettling secrets in his own family history, and to reveal the tragedy that fueled his grandfather’s relentless experimentation—experimentation that would revolutionize our understanding of ourselves. Dittrich uses the case of Patient H.M. as a starting point for a kaleidoscopic journey, one that moves from the first recorded brain surgeries in ancient Egypt to the cutting-edge laboratories of MIT. He takes readers inside the old asylums and operating theaters where psychosurgeons, as they called themselves, conducted their human experiments, and behind the scenes of a bitter custody battle over the ownership of the most important brain in the world. Patient H.M. combines the best of biography, memoir, and science journalism to create a haunting, endlessly fascinating story, one that reveals the wondrous and devastating things that can happen when hubris, ambition, and human imperfection collide.