Chemical weapons enter modern warfare in 1915, when chemist Fritz Haber, a Nobel laureate, helps Germany deploy chlorine gas against Allied trenches, killing and maiming thousands in an attack that unnerves even the soldiers who unleash it. Narrator Graham Templeton traces the weapon's path forward from there: mustard gas in the trenches of World War I, the Geneva Protocol's 1925 ban on their use, and the treaty's repeated failure to hold. Agent Orange gets sprayed across Vietnam's jungles for its defoliant properties, its effects on soldiers and civilians largely dismissed at the time. Sarin turns up in the Iran-Iraq War, and chlorine again in Syria decades after it first entered the battlefield. Interviews and archival footage carry the case that the ban created by these weapons' visible horror has never actually stopped their production or use, only pushed nations and armed groups to keep testing where the line holds. The film treats the weapons as a recurring bargaining chip between deterrence and atrocity, one that keeps resurfacing whenever the world assumes it has been retired.