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. The composer Michał manages to telephone his wife and child in another part of the city that is being overrun by the Germans. After a few words, she tells him that the Germans are clearing the building and that they are coming for her. Then the line goes dead. The next morning, 23-year-old Officer Cadet Korab apologizes after walking into a room to find the second in command, Lieutenant Mądry, and messenger girl Halinka in bed together. A German attack is stopped, but Korab is wounded while disabling a Goliath tracked mine. Surrounded by the enemy, Zadra is ordered to retreat through the sewers to the city centre. Now down to 27 fit to travel, including Korab, they slog through the filth. Daisy, their guide, asks Zadra to let her help Korab, claiming that the others can find their way easily enough. Zadra consents. However, the pair fall further and further behind. When they reach the designated exit at Wilcza Street, Korab is too weak to climb the upward sloping tunnel, so they rest for a while. He notices some graffiti on the opposite wall, but cannot quite make it out. Daisy tells him it says "I love Janek", when the name is actually Jacek, Korab's first name. She decides that they should head in the direction of the river, which is only a short distance away and drives him on, not letting him stop. Finally, they see sunlight. By this time, Korab is half blind and at the end of his strength. He cannot see that the exit is closed off by metal bars. Daisy finally reveals her feelings for him, kissing him before telling him that he can rest for a while. The main group follows Zadra for a while, but they become lost without Daisy. Finally, when Zadra tells Sergeant Kula to order them onward after a brief rest, they remain where they are. Kula lies and tells Zadra they are following in order to get him to keep going. Eventually, the only remaining soldier following Zadra and Kula is the mechanic Smukły. Meanwhile, Mądry, Halinka and Michał are also lost. Eventually, Michał loses his mind and wanders away, playing an ocarina. Upon reaching a dead end, Mądry cries out that he has somebody to live for. When Halinka asks who, he tells her that he has a wife and child. She asks him to turn off his flashlight, and then shoots herself. Mądry finds an exit, but as soon as he has climbed out of the sewer he is disarmed by a German soldier. He looks around the courtyard he has emerged into and sees others who have come though the same manhole standing in silence guarded by armed German soldiers. Some are lined up against a nearby wall that is stained with blood. Despondent, he kneels beside the bodies of others who have already been executed. Zadra, Kula and Smukły miss the exit at Wilcza Street but find another - however it is booby trapped. Smukły disarms two German grenades, but is killed by the third and last. Zadra and Kula emerge from the sewer to find themselves in a deserted part of the ruined city. When Zadra tells Kula to bring up the rest of the men, Kula admits he lied and that they left them behind a long time ago. Enraged, Zadra shoots Kula and reluctantly heads back down into the sewer to search for his men.
