The Milewskis are a middle-aged couple. Witold and Magda, both occupied with careers in managerial positions, create a solid, well-matched relationship. They have no children - this is Magda's decision, who preferred to pursue a career rather than take care of diapers. However, little remains of the bond they had at the beginning. Each Sunday, each of them cheats on their partner, and they both know nothing about it. Everything changes when Witold's younger brother Franek, a handsome geologist, shows up at their place.