It is 25 September 1944, during the last days of the Warsaw Uprising. Lieutenant Zadra leads a unit of 43 soldiers and civilians to a new position amidst the ruins of the now isolated southern Mokotów district of Warsaw.
A Generation is set in Wola, a working-class section of Warsaw, in 1942 and tells the stories of two young men at odds with the Germans occupation of Poland. The young protagonist, Stach (Tadeusz Łomnicki), is living in squalor on the outskirts of the city and carrying out wayward acts of theft and rebellion. After a friend is killed attempting to heist coal from a German supply train, he finds work as an apprentice at a furniture workshop, where he becomes involved in an underground communist resistance cell guided first by a friendly journeyman there who in turn introduces Stach to the beautiful Dorota (Urszula Modrzyńska). An outsider, Jasio Krone (Tadeusz Janczar), the temperamental son of an elderly veteran, is initially reluctant to join the struggle but finally commits himself, running relief operations in the Jewish ghetto during the uprising there.
Five young men who have lost their ideals during the Nazi occupation make a living on stealing. After they have been caught and convicted they try to become legit. Hereby they encounter a variety of problemes including getting unwillingly entangled in plans of terrorists.
Marta Weiss (Barbara Drapinska), a Polish Jew, arrives by cattle car to the Auschwitz concentration camp. While there she catches the attention of the guards as she is multilingual and is put to work as a translator. When she inquires about the factory at the camp a fellow inmate informs her it is a crematorium and that the rest of her family has likely been murdered.
Arye and his daughter Itke are musicians, or klezmorim, who became impoverished and were evicted from their home in Kazimierz. Arie sees no choice but to embark on a career of a travelling band, but fears for the safety of his daughter on the dangerous roads. Itke solves the problem by disguising herself as a boy and adopts the persona of "Yidl", ostensibly Arie's son. During their voyages, they meet another pair of merrymakers, the father-and-son duo Isaac and Ephraim Kalamutker, with whom they form a quartet and roam through the Polish countryside seeking engagements. "Yidl" falls in love with Ephraim, who is utterly oblivious to the true sex of his companion. The four are hired to perform in the wedding of young Teibele to the old, rich man Zalman Gold. The bride had to cancel her prior engagement with her true love, Yosl Fedlman, for her late father left many unpaid debts. Yidl takes pity on Teibele and the quartet smuggle her out of the party and have her join them as vocalist. To Yidl's dismay, Ephraim is enamored with the young woman. Itke reveals her true self to Isaac, who determines to assist her and leaves to locate Yosl. When arriving in Warsaw, the group become a success and are hired to perform in a concert. However, personal tensions between the members run high. Efraim signs a contract with a local orchestra. Teibele's lost match finally arrives, and they run off together before the show. Yidl, quite by accident, takes her place and recounts her entire story and love for Efraim in song form. She is applauded and signed on a contract for a career in the United States. Having learned the truth, Efraim abandons his commitments and joins her on the ship to New York.