In the southern town, a gang of "currency traders" is operating, led by the Chief and his assistant Kozodoyev. A modest Soviet clerk and an exemplary family man Semyon Semyonovich Gorbunkov goes on a foreign cruise on a motor ship, on which Kozodoyev also sailed, who must pick up diamonds in one of the eastern cities and transport them in a plaster hand. But due to a misunderstanding, instead of a swindler, an unsuspecting Gorbunkov falls in the appointed place, and a precious plaster is imposed on him. That's where it all starts...