Autumn 1943. An enemy shepherd dog attacks a Soviet reconnaissance group during a sortie. Defending themselves, the soldiers open fire, giving away their location and coming under mortar fire. Having narrowly escaped death, the head of the Gromov reconnaissance group takes the injured dog with him and asks the surgeon to perform surgery on her and save the animal.
When the dog recovers, Gromov is going to reform him and unsuccessfully tries to establish contact with him. Corporal Miroshnikov helps the hero find a common language with the dog. Soon, thanks to kindness and ingenuity, he manages to turn the dog into an assistant who is ready to go with him on exploration and perform difficult tasks. But one day Gromov meets the former owner of Rex, who tries to force the dog to remember old habits and commands.…
