Kulski, the son of the Deputy Mayor of Warsaw, is a 10-year-old Boy Scout when the Germans invade Poland in September 1939. He soon begins waging his own private war against the Germans with small acts of sabotage. At age 12, Kulski is recruited into the clandestine Underground Army by his Scoutmaster and begins training in military tactics and weapons handling. At 13, he accompanies his commander on a secret mission into the Warsaw Ghetto to liaise with the leaders of the Jewish Resistance.

Arrested by the Gestapo at age 14, Kulski is incarcerated in the notorious Pawiak Prison, beaten, interrogated at Gestapo headquarters, and sentenced to Auschwitz. After being rescued, he joins the Ninth Commando Company of the Underground Army, and at age 15 fights in the Warsaw Uprising of 1944.

Taken prisoner by the Germans, 16-year-old Kulski ends the war in a POW camp, finally risking a dash for freedom onto an American truck instead of waiting for "liberation" by the Soviets.