Captain Terence Stevenson with the British Army is part of the bomb disposal unit in London, his primary job to defuse them. Despite having no experience as a spy, he is asked by his superiors, because of his academic background as a chemical engineer and being fluent in Romanian and German, to lead a spy mission deep in Nazi occupied territory. The Nazis have near perfected a formula for a new poisonous gas to use in chemical warfare, his mission to infiltrate the gas plant near Pilsen in Czechoslovakia where it is being mass produced, steal the formula to bring back to Britain, and blow up the plant before the Nazis are able to distribute the gas for their war effort.