The film concerns an idealistic young teacher, Carla Nowak, who teaches 7th graders at a German gymnasium which has been plagued by a series of thefts.

Early in the film, we see Nowak challenge her students to decide whether 0.999... = 1, and brings up the difference between a proof and an assumption. Her favorite student, Oskar Kuhn, presents the standard argument from 0.111... = 1/9, but most of the class still doesn't seem to get it. Nowak brings the discussion to a somewhat rushed conclusion by explaining that "a proof needs a derivation that builds up step by step." However, no one manages to question whether Oskar's argument itself relies on some unproven assumptions; why, after all, do we know that 0.111... = 1/9?

In my interpretation, the weakness of Nowak's presentation foreshadows the challenges she faces for most of the film, after she rushes to accuse a co-worker of theft on the basis of a video she had surreptitiously recorded on her laptop. The video captures a person's arm, wearing a distinctive blouse, reaching into Nowak's pocket for her wallet. The only person in the office wearing such a blouse is apparently the receptionist, who is also Oskar's mother. But as Frau Kuhn herself immediately points out to the principal, they have no definitive proof that she was really the only one wearing that blouse at the time. This small doubt festers in Nowak's conscience for the rest of the film, as the standard of argument on all sides quickly deteriorates into scapegoating and innuendo.