In 1943, after the defeat at Stalingrad and Kursk, Nazi Germany decided to use chemical weapons prohibited by all international conventions. In the occupied territories of Western USSR preparations for tests on Soviet prisoners of war began in secrecy. Among them was lieutenant-gunner Sergey Gromov, who managed to escape the attack on a convoy of guerrillas. He's trying to get in touch with the underground and goes to Anna - a German translator associated with the underground. After checking, Sergei, together with other members of the underground, kidnaps a German scientist - Professor Eberle, but he is killed by a stray bullet. Survived Sergei, Anna and a radio operato Savchenkor, dressed in German uniforms, steal a truck with shells and go to the front line to pass the shells to unknown agents.