A group of old friends have a tradition of going to a public bathing house on New Year's Eve. Occasionally too much vodka and beer makes two of them unconscious. The problem is that one of them (Sasha) has to go to Leningrad but another one (Zhenya) goes. Zhenya wakes up at Leningrad airport. Believing that he is still in Moscow he takes a taxi and goes home. The street name, building and even apartment number, the way an apartment complex looks the same and the key coincide completely - just typical Soviet-type 'economy' architecture. Imagine the surprise of Nadya when she enters her apartment and finds a man without trousers in her bed. What's more - Nadya's fiancé also finds him there...

Zhenya and Nadya go their separate ways. Nadya stuck with her bureaucrat boyfriend, married him and had a daughter, also called Nadya. Zhenya married and had a son, Konstantin. Both later divorced. More than 30 years later, Konstantin ends up drunk in the flat where the younger Nadya finds him. He is there as part of a convoluted ruse by his father's friends to get Zhenya back into the arms of the woman with whom he shared a magical night. The waylaid son is the bait to get Zhenya back to Leningrad, now called St. Petersburg. One romance is rekindled and another between the son and daughter is struck up.