Ukrainian and now British spy Hryhoriy Didenko returns to his native town of Novohrad-Volynsky after 15 years with a top-secret mission – to obtain a sample of Tabun's newest chemical weapon for the development of an antidote. The obstacles for Grigory will be not only the Nazi regime and deadly gas, but also the distrust of the local residents, whom he is trying to save from the ever-increasing threat.