The film begins with a sequence (supplemented by subsequent flashbacks) in which Mikhail Kalashnikov (Yuri Borisov), a young farmer's son from Altai, is seen secretly working on a functional toy rifle. The film switches to the year 1941, in the midst of World War II, where the now adult senior sergeant Kalashnikov serves as a tank commander in the Red Army. During the Battle of Bryansk, Kalashnikov is seriously wounded while taking out a German anti-tank gun, and he is taken off the front-lines. While being transported to the rear, he and a companion encounter a group of German soldiers, and he witnesses his comrade's new sub-machine gun failing at a critical moment due to design faults in the magazine (the mag got filled with water and when the water froze, it froze the bullets. The spring was too weak to keep all the bullets nicely separated). This inspires him to use his self-acquired talent at inventing to design a new automatic weapon for the Soviet army.

On his way home (he was sent home to recover), Kalashnikov visits Matai Station in Kazakhstan, where he previously worked as an engineer but was dismissed for using the depot's workshop to build his private weapon designs. He appeals to his former superior, & the head of the depot Krotov (Sergey Gazarov), to let him assemble his latest invention, but Krotov refuses. When Kalashnikov proposes his design to a passing high-ranking officer named Basarov (Seydulla Moldakhanov), he gets authorization to proceed, and with the help of the workers (Kuzmich (Yuriy Loparyov), Kravchenko (Mikhail Gudoshnikov), uncle Misha (Aleksandr Nikolsky) all of whom work in their spare time) he successfully assembles his new sub-machine gun.