In turn-of-the-century Budapest, two groups of teenage boys engage in a mock war over one of the few vacant lots remaining in the city. The Paul Street boys have long regarded the lot as their exclusive property; now the fearsome Red Shirts have decided to drive them out and take over. As preparations begin for the battle and each side plans its strategy, Private Nemecsek, the smallest, youngest, pluckiest Paul Street boy, aspires to becoming an officer. Spying on the Red Shirts, he is forced to hide in the water to avoid discovery and catches cold. Then, when Gereb, a Paul Street boy, defects to the Red Shirts, Nemecsek sneaks into the enemy camp to find out what secrets the traitor has divulged. Hearing the Red Shirts disparaging his comrades, Nemecsek speaks out in their defense and is thrown into a lake. As a result, Nemecsek falls ill with pneumonia, much to the concern of Boka, the general of the Paul Street boys, who has become fond of the small but courageous private. Finally, the battle formally begins. Although gravely ill, Nemecsek gets out of bed and goes to the battlefield, determined to fight.