Poison gas enters modern warfare in the trenches of the First World War, and this film traces the science behind it from that first recorded use through the chemical arsenals later built and deployed by twentieth-century dictators and terrorists. It follows the chain from laboratory to battlefield, showing how research meant to solve practical military problems produced weapons whose effects went far beyond any single engagement. The film treats chemical warfare as a case study in a larger pattern: military demand pulling scientific knowledge toward destructive ends, then that knowledge outliving the war that produced it and resurfacing in later conflicts and attacks. Archival material from the Great War anchors the historical sections before the film moves forward into more recent uses of gas as a weapon of terror and state violence. The throughline is the relationship between scientists and armies, and how that partnership has kept reshaping the tools available for war.