Moscow, June 1941. Nina Sinitsyna and Ilya Borisov live on opposite sides of a stairwell landing in an apartment building; she, the daughter of a seamstress, in a crowded "kommunalke" ("communal apartment"), and he, a medical student and the son of a famous surgeon, in a spacious, private, single-family apartment. They are deeply in love, but, enforcing the rigid class boundaries of this "classless society", their parents have forbidden them to see each other. Still, they hope to marry, and often secretly meet. Suddenly, Nazi Germany treacherously attacks Russia, and the Great Patriotic War (WWII) begins. Ilya`s father soon leaves for the front to oversee a hospital train that provides medical care for wounded soldiers, while Ilya continues medical school in Moscow. Nina joins the service and trains to become a "prozhektorist", an anti-aircraft searchlight operator.