Based on the novel of the same name by Yurii Mushketyk. For the second year, a laboratory headed by professor Marchenko has been working on the problem of photosynthesis. The work absorbs the entire team – each new result seems to confirm the correctness of the leader’s theory. The scientist Borozna, convinced that his colleague’s research path is mistaken, makes it clear to a doctor that it is time to stop and take a more critical look at the results.