Susannah Cahalan is the award-winning, New York Times bestselling author of Brain on Fire: My Month of Madness, a memoir about her struggle with a rare autoimmune disease of the brain. She writes for the New York Post. Her work has also been featured in the New York Times, Scientific American Magazine, Glamour, Psychology Today, and other publications. Her latest book, The Great Pretender: The Undercover Mission That Changed Our Understanding of Madness (Grand Central Publishing) is a propulsive narrative history investigating the 50-year-old mystery behind a dramatic experiment that changed the course of modern medicine. For centuries, doctors have struggled to define mental illness–how do you diagnose it, how do you treat it, how do you even know what it is? In search of an answer, in the 1970s a Stanford psychologist named David Rosenhan and seven other people–sane, normal, well-adjusted members of society–went undercover into asylums around America to test the legitimacy of psychiatry’s labels. Forced to remain inside until they’d “proven” themselves sane, all eight emerged with alarming diagnoses and even more troubling stories of their treatment. But, as Cahalan’s explosive new research shows, very little in this saga is exactly as it seems. What really happened behind those closed asylum doors, and what does it mean for our understanding of mental illness today?