Two young people - a medical student Busygin and a sales agent Semyon, nicknamed Silva - were struck by strangers. After escorting them home, but not meeting the further hospitality they were counting on, they discover that they were late for the train. Time later, it’s cold outside, and they are forced to seek shelter in a strange area. Young people themselves are barely familiar, but misfortune brings them together. Both of them are guys with humor, they have a lot of enthusiasm and games, they do not lose heart and are ready to take every opportunity to keep warm.
They knock on the house of a lonely thirty-year-old woman Makarska, who had just banished the tenth-grader Vassenka in love with her, but she also sews them off. Soon, the guys who do not know where to go see how an elderly man from the neighboring house, who called himself Andrei Grigorievich Sarafanov, hails her. They think that this is a date, and decide to take the opportunity to visit him and keep warm a little in the absence of Sarafanov. At home they find the upset Vasenka, the son of Sarafanov, who is experiencing his love failure. Busygin pretends to have known his father for a long time. Vassenka is very wary, and Busygin is trying to inform him, saying that all people are brothers and we must trust each other. This leads the cunning Silva to the idea that Busygin wants to play the kid by introducing himself as Sarafanov’s son, Vasenka’s half-brother. Inspired by this idea, he immediately plays along with a friend, and the dumbfounded Busygin, who did not have this in mind at all, appears to Vasenka as his unknown elder brother, who finally decided to find his father. Silva is not averse to developing success and inclines Vasenka to celebrate the event - to find something from the alcohol bins and drink to celebrate his brother’s acquisition.
While they are celebrating in the kitchen, Sarafanov suddenly appears, going to Makarskaya to ask for his son, drying out of love. The hopped-up Vasenka enchants him with stunning news. Confused Sarafanov at first does not believe, but, remembering the past, nevertheless admits such an opportunity - then the war only ended, he was "a soldier, not a vegetarian." So his son could be twenty-one years old, and his mother's name was ... her name was Galina. These details are heard by Busygin peering out of the kitchen. Now he is more confident in meeting with his imaginary father. Sarafanov, questioning the new-born son, is more and more confident that before him is really his offspring, sincerely loving his father. And Sarafanov now just needs such love: the youngest son fell in love and strives to get out of hand, his daughter gets married and is going to Sakhalin. He himself left the symphony orchestra and plays at dances and at a funeral, which he proudly hides from children, who are nevertheless aware and only pretend that they know nothing. Busygin plays his role well, so even the adult daughter of Sarafanov, Nina, who initially met her brother very incredulously, is ready to believe.
Sarafanov and Busygin spend the night in confidential conversation. Sarafanov tells him his whole life, reveals his soul: his wife left him, because it seemed to her that he played the clarinet for too long in the evenings. But Sarafanov is proud of himself: he did not allow himself to dissolve in the bustle, he composes music.
In the morning, Busygin and Silva make an attempt to slip away imperceptibly, but encounter Sarafanov. Upon learning of their departure, he is discouraged and upset, he gives Busygin a silver snuff box as a keepsake, since, according to him, in their family she always belonged to her eldest son. The moved impostor announces his decision to linger for a day. He helps Nina clean the apartment. A strange relationship is established between him and Nina. It seems that they are brother and sister, but their mutual interest and sympathy for each other clearly do not fit into the family framework. Busygin asks Nina about the bridegroom, involuntarily releasing jealous taunts against him, so that between them there is something like a quarrel. A little later, Nina will also jealously respond to Busygin’s interest in Makarska. In addition, they constantly turn to talk about Sarafanov. Busygin reproaches Nina for going to leave her father alone. They are also worried by brother Vasenka, who continually tries to escape from home, believing that no one here needs.
Meanwhile, Vasenka, encouraged by the unexpected attention of Makarska, who agreed to go to the cinema with him (after talking with Sarafanov), comes to life and is now not going to go anywhere. However, his joy does not last long. Makarska is scheduled to meet with Silva who has attracted her for ten hours. Upon learning that Vasenka bought a ticket at the same time, she refuses to go, and naive obstinacy indignantly admits Vasenkino that the boy owes her unexpected kindness to his dad. In desperation, Vasenka collects the backpack, and the sensitive Busygin, who had just intended to leave, is again forced to stay.
In the evening, Nina's pilot Kudimov appears with two bottles of champagne. He is a simple and open guy, dubious and perceiving everything too straightforwardly, which he is even proud of. Busygin and Silva now and then make fun of him, to which he only smiles good-naturedly and offers a drink so as not to waste time. He’s barely enough, he, the cadet, doesn’t want to be late, because he promised himself never to be late, and his own word is law for him. Soon Sarafanov and Nina appear. The whole company drinks for an acquaintance. Kudimov suddenly begins to remember where he saw Sarafanov, although Busygin and Nina
they try to stop him, convincing that he could not see him anywhere or saw him at the Philharmonic. Nevertheless, the pilot with his inherent principles persists and in the end recalls: he saw Sarafanov at the funeral. Sarafanov bitterly forced to admit it.
Busygin reassures him: people need music both when they have fun and when they yearn. At this time, Vasenko with a backpack, despite attempts to stop him, leaves his home. Despite her persuasion, Nina’s bridegroom, too, is torn away, being afraid to be late for the barracks. When he leaves, Nina rebukes the malicious brother that he treated her fiancé badly. In the end, Busygin can’t stand it and admits that he is not his brother Nina at all. More than that, he seems to be in love with her. Meanwhile, offended Sarafanov collects a suitcase to go with his eldest son. Suddenly runs in with a startled-solemn look of Vasenka, and after him Silva in half-burnt clothes, with a soot-stained face, accompanied by Makarska. It turns out that Vasenka set fire to her apartment. Outraged Silva demands trousers and, before leaving, in the doorway vindictively reports that Busygin is not a Sarafan son at all. This makes a great impression on everyone, but Sarafanov firmly declares that he does not believe. He does not want to know anything: Busygin is his son, and, moreover, his beloved. He offers Busygin to move from the hostel to them, although this is met with an objection by Nina. Busygin reassures him: he will visit them. And then he discovers that he was late for the train again.
