Zofia (Maria Koscialkowska) is an ethics teacher who lives alone. Her husband died years ago, and her son is far away. Arriving for her classes at the University of Warsaw, she meets Elzbieta (Teresa Marczewska), a translator of her books from New York. They had spent some time together in America a while back. Elzbieta is in Poland doing a research project on the fate of Jews who survived World War II. She asks to sit in on Zofia's classes.

A student offers an ethical dilemma for consideration; it revolves around a doctor, a pregnant woman, and her dying husband (the story portrayed in The Decalogue II). When Zofia comments that nothing is more important than the life of the child, Elzbieta asks if she can tell a true story that happened in 1943 Warsaw. A six-year-old Jewish girl is taken to a Catholic couple who have promised to be her godparents in order to protect her from the Nazis. But at the last minute the woman says that they cannot lie about such a serious matter, that to be parties to a fake christening would be bearing false witness to the God they believe in. This action puts the child's life in grave danger.

In this gripping dramatic treatment of "Thou shalt not bear false witness" Krzysztof Kieslowski examines the impact our words and deeds have upon others. It turns out that Elzbieta and Zofia are the main characters in the story from 1943. The former was grievously wounded by this incident and has been haunted and humiliated ever since because the couple did not rescue her. Zofia was the one who refused to lie to protect her, and she has lived with guilt about this decision for forty years.

The two women do a slow dance of remembering together. They even visit Zofia's old apartment where the fateful events took place. The ethics professor explains the real reason behind her refusal to shelter Elzbieta; she and her husband, leaders in the resistance, believed a falsehood about the couple who were to take the Jewish child next. Reaching across the abyss of time, the two women confront their inner demons. With grace, they purge the past and open the door to a fresh future. Words — our witnessing — can kill, says Kieslowski, but they can also bring healing and a restoration to life.