According to the plot of the cartoon, a dog named Faithful is the only one who remains alive after the treacherous attack of the horde of the Crimean Khan Devlet Giray on one of the fortified prisons of the Bolshaya Zasechnaya Line. His task is to bring the news of the approaching disaster to Tula. Faithful sets out on a journey and, with the help of friends, fulfills his dangerous mission.