Historian Dan Snow spends three episodes tracing the grime, waste, and disease that shaped medieval London, industrial New York, and revolutionary Paris. In London, he wades into the sewage-choked streets of the fourteenth century, handles the tools used to collect human waste for tanning and dyeing, and follows the Black Death's path through overcrowded parishes. New York's episode tracks the filth of the Gilded Age, from horse manure piled in the streets to the slaughterhouses and tenements that bred cholera outbreaks. Paris gets the revolutionary treatment, with Snow examining the squalor of pre-revolution streets that helped fuel the uprising against the monarchy. Reenactments, animated diagrams, and visits to archives and surviving locations back up the narration, and Snow repeatedly gets physically involved, handling waste, tools, and period materials rather than just describing them. The series argues that sanitation, or the total absence of it, drove political upheaval and public health disasters as much as any king, revolution, or robber baron did.