A group of scientists is sent to the planet Arkanar to help the local civilization, which is in the Medieval phase of its own history, to find the right path to progress. Their task is a difficult one: they cannot interfere violently and in no case can they kill. The scientist Rumata tries to save the local intellectuals from their punishment and cannot avoid taking a position.

Military doctor General Klenski is arrested in Stalin's Russia in 1953 during an anti-Semitic political campaign accused of being a participant in so-called "doctors' plot".

Rookie Alexey Gavrilov ends up in a unit where hazing reigns. He resists as much as he can to the three "grandfathers" who, on the eve of demobilization, decide to recoup as much as possible on the "turtles" for past humiliations. He soon finds a like-minded person. Unable to break the will of the obstinate, the "grandfathers" carry out a vile provocation, and then Alexei decides to take a desperate step.

The self-taught inventor Kostylin, convinced of the expediency of his latest work, this time decided to seek recognition to the end.