The Italian soldier Giuseppe Santucci, on his way home from the Russian front, during World War II (in 1943), has his machine gun stolen in Warsaw. Afraid of consequences, he stays in Warsaw and occupies a flat of the Polish girl Maria, whom he suspects of stealing weapon. Maria indeed is an active member of the Polish resistance, contrary to her brother, Staszek, a painter, who only wants a calm living. In a course of funny events, Giuseppe falls in love, and, along with Staszek, becomes a hero of the Polish resistance.