Ukrainian, and now British intelligence officer Grigory Didenko, after 15 years returns to his hometown of Novograd-Volynsky with a top-secret mission - to obtain a sample of the latest Tabun chemical weapons for the development of an antidote. Obstacles for Gregory will be not only the Nazi regime and the deadly gas, but also the distrust of the local residents, whom he is trying to save from the growing threat.