The Black Death killed an estimated 25 million people across medieval Europe, but the English village of Eyam offers a strange counter-example. When plague arrived there in 1665, the villagers sealed themselves off from the surrounding countryside rather than flee, a self-imposed quarantine that likely saved neighboring towns while killing most of Eyam itself. The film follows scientists and historians examining why some residents survived repeated exposure while others died within days, tracing the search for a genetic explanation down to descendants still living in the village today. Interviews with researchers lay out the case for inherited immune variations, including mutations that may have blocked the infection at a cellular level, and connect that same genetic quirk to modern disease resistance. Village records, parish histories, and the physical layout of Eyam itself, including the boundary stones where outside families left food and supplies, ground the science in a specific, documented act of collective self-sacrifice.