The events of the Russian military-historical series "Apostol" take place in 1942. Twin brothers Pasha and Petya Istomin haven't seen each other in a long time: life has taken them to different parts of the country. Pavel becomes an enemy of the people and falls under a tribunal. Peter stays in their hometown and teaches math to schoolchildren. When his brother dies while attempting to escape from a camp, he is taken under the control of the NKVD. Captain Khromov makes the decision to use the brothers' external resemblance and recruit Istomin.