Dioxin has no known safe exposure level, and this investigation traces how it became a hidden hazard in 1990s Britain, linked by researchers to heart attacks, liver disease and neurological damage. The film follows the trail back to the chlorine industry, examining incinerators, factories and waste sites where the chemical byproduct accumulated largely unchecked by regulators. Interviews with scientists, campaigners and former industry insiders lay out how dioxin entered the food chain and the water supply, and how slowly official bodies moved to measure or contain it. Archive news footage from the period captures the public alarm as contamination scares hit headlines, while present-day interviews reassess what was actually known at the time versus what industry downplayed. The film treats this as an unresolved warning rather than a closed case, asking what continued vigilance would actually require. It builds a picture of institutional negligence pieced together from documents, testimony and case studies of communities near contaminated sites, making the abstract chemistry of dioxin concrete through the people who lived with its consequences.