On 8 May 1945, at the end of World War II, near a small country church, former Home Army soldiers Maciek Chełmicki Zbigniew Cybulski, Andrzej Kossecki Adam Pawlikowski and Drewnowski Bogumił Kobiela prepare to assassinate Konrad Szczuka, a political opponent and secretary of the Polish Workers' Party. Their ambush fails, and the trio soon discovers they have mistakenly killed two innocents.
Major Waga Ignacy Machowski learns of the failed attempt and orders a second try. The three head to the Hotel Monopol Restaurant, where a victory banquet is underway but the combatants themselves remain on the sidelines. In the bar, Maciek and Andrzej listen to the song The Red Poppies of Monte Cassino and reminisce about their fallen comrades. To honor their memory, Maciek lights several glasses of rectified spirit on fire. Drewnowski, utterly drunk, moves among the guests and discusses postwar career prospects in Poland with Pieniążek Stanisław Milski, a representative of the democratic press.
During the party, Maciek becomes drawn to Krystyna Rozbicka Ewa Krzyżewska, the barwoman, and invites her to his room. After a tense moment there, Krystyna joins him later, and they lie together, realizing they are in love. Yet Krystyna fears attachment, sensing that Maciek does not plan to stay in town for long. They decide to take a walk instead, and when rain begins to fall, they shelter inside a ruined church. Krystyna notices a poem inscribed on the wall, and Maciek recites it from memory. They say their goodbyes, with Maciek promising to change his situation so he can stay with her.
Back at the bar, Maciek discusses his sense of duty and obligation to the cause with Andrzej Kossecki; Andrzej remains unsympathetic, arguing that Maciek would be a deserter if he does not fulfill his obligation to assassinate Szczuka. Meanwhile, a completely inebriated Drewnowski ruins the banquet, spraying foam from a fire extinguisher and leaving the celebration in clouds of confusion. He later confronts the idea of career advancement as a Communist functionary with Marek Szczuka, the son of Szczuka who is connected to the underground.
After the reception, Szczuka learns that his son Marek Jerzy Jogałła has been arrested for joining an underground militia. Maciek waits for Szczuka to leave the hotel to meet his captured son, follows him, and shoots him to death. The following morning, Maciek plans to depart Ostrowiec by train. He tells Krystyna of his decision to leave, and she is left heartbroken by the news. The hotel guests dance to a pianist and band playing Chopin's Military Polonaise in A Major.
On the way to the train station, Maciek observes Andrzej beating Drewnowski for his opportunistic support of the underground. Panicked, Maciek flees when Drewnowski calls his name. He briefly encounters a squad of soldiers from the Polish People’s Army, draws his pistol in a moment of fear, and is fatally wounded. He staggers to a garbage dump, collapses, and dies, leaving behind a quiet, tragic reflection on duty, love, and the costs of war.
