The movie opens at a military function where an old veteran intervenes to save a dog from a cruel soldier, leading to a conversation about humanity's cruelty versus a dog's loyalty. The story then flashes back to 1939, focusing on Volkov, a skilled pilot who has an affair with the General's daughter, Tatiana, and faces severe consequences, including a two-year prison sentence. After his release, he becomes a forest ranger and rescues a puppy he names Prince.

In 1943, as the war intensifies, Volkov and Prince fight side by side. Volkov is injured during a German bombing, and his fiancée, Nina, helps him recover. Meanwhile, he learns of Tatiana's unhappy marriage. As the Germans advance, Volkov undergoes military dog training, but he’s horrified to discover that the dogs are being sent on suicide missions beneath tanks.

Despite his fears, Volkov chooses to fight for his country, and during a battle, several dogs, including Prince, are sent to destroy enemy tanks. Tragedy strikes as their missions result in losses for both sides. In a climactic moment, Prince sacrifices himself to save Volkov and Nina, leading to a devastating explosion.

Back in the present, the old veteran reveals that his mother died shortly after the war, and his father, Volkov, became a successful pilot but went missing in action. The veteran was adopted by Tatiana, who shared the heroic stories of Volkov and Prince.