Once upon a time, young scientists Kalitin and Danilov were friends, but a quarrel separated them. The circumstances of the quarrel remained unclear to everyone until the end. But everyone thought they were right. Years have passed. Professor Kalitin’s son, working under his leadership, moves to the institute headed by Danilov. Kalitin learns about this decision of Igor on the day of the arrival of his friend and colleague Vasin. On this occasion, old friends gather at the professor’s house, including Luzgin, Kalitin’s boss. Reflections on his life help the professor understand his son’s choice, oppose the unprincipled careerist Luzgin and make peace with Danilov.