Dr. Michael Mosley traces the history of experimental psychology, much of it built on experiments that would never pass an ethics board today. He revisits the era of behaviorists who believed the mind could be engineered like a machine, including the conditioning studies that shaped childhood fears and the isolation experiments used to strip subjects of their sense of self. Mosley puts himself through recreations of several of the key experiments, from sensory deprivation to obedience tests modeled on Milgram's work, to show what the original subjects actually endured. Archive footage and interviews with psychologists fill in the era's confidence that human behavior could be predicted and controlled, and the human cost when that confidence went unchecked. The series treats the scientists as neither villains nor heroes but as people chasing a hard question: what actually shapes who we become? It is a history of psychology told through its most brutal methods, and a reminder of how recently the field's ethical guardrails were built.