The Great Patriotic War. Soviet intelligence officers led by Sergei Skorin and Andrei Losev are trying to track down a well-trained sabotage group that is staging large-scale sabotage in the rear of the Red Army on the eve of the Battle of Kursk. Andrey and Sergey are brothers, but there has been a conflict between them for many years. Andrey does not trust Sergei, because he suspects that his brother has been turned upside down.