Neurologist V. S. Ramachandran argues that rare cases of brain damage, long dismissed as medical curiosities, can reveal how the healthy brain builds a sense of self. This episode, the first of a five-part BBC series, examines patients with phantom limb pain, anosognosia, blindsight, and hemispatial neglect. Ramachandran walks through the clinical picture of each condition: a woman who cannot see anything on her left side yet can still navigate around it, a man who denies his paralyzed arm is paralyzed, an amputee who feels a limb that is no longer there. Rather than relying only on scanners, Ramachandran improvises simple tools, mirrors, cotton swabs, everyday objects, to test what these patients can and cannot perceive, turning bedside observation into an experiment. The throughline is that these disorders are not just malfunctions but windows into the machinery that normally stitches body, vision, and identity into one seamless experience. When that machinery misfires, the film uses each patient's account to ask what the brain is doing the rest of the time to keep it from happening to everyone else.