The narration is on behalf of the father.

Near Moscow, a father, mother Marusya and their daughter, six-year-old Svetlana, rent a summer house. Father and daughter dream of swimming, fishing, picking berries, but Marusya first makes them clean up the cottage.

When all things are done, her old friend, a polar pilot, comes to visit Marusa. Maroussia spends all day with him, and then goes to accompany him to the station. Father and Svetlana hang on the roof a makeshift pinwheel of colored paper. Returning Maroussia is unhappy that Svetlana is still not sleeping and is sitting on the roof. Despite the gifts brought by the mother, the father and daughter go to bed offended.

In the morning, Maroussia accuses her husband and daughter of breaking her blue cup. Maroussia leaves for the city, and father and Svetlana decide to go wherever they look.

On the way, they meet the neighbor boy Sanka. Sanka complains that the pioneer Pashka wants to beat him. Svetlana promises Sanka protection. Soon, travelers meet Pasha, who calls Sanka a fascist. From Germany, fleeing from the Nazis, came a Jewish worker with his daughter. Pashka stood up for the girl, which Sanka insulted. The outraged father and Svetlana are supported by the collective farm watchman: there are no fascists under the Soviet regime. Sanka repents.

The watchman advises his father and Svetlana to go to the lake, where there is a pine forest - his daughter Valentina and grandson Fedor live there.

On the way, travelers give flowers to some grandmother, who treats them with cucumbers and bathes in the river. Finally, they get to Valentina’s house, where they are cordially invited to relax in the garden under an apple tree.

Father tells Svetlana how they met Marusya. During the Civil War, his father saved Marusya from the whites, and he, the wounded, took care of Marusya. Since then, they have not parted. The father is worried: suddenly Marusya no longer loves him, but Svetlana reassures her father. At night, she noticed with what love Maroussia looked at him.

Valentina finds a cart so that travelers can get to the house, and Fedor goodbye gives Svetlana a kitten.

At home they are met by the laughing Maroussia, who managed to climb onto the roof and straighten the turntable.

In the evening, a happy family sits at a table for a long time. They tell each other what they saw during the day. And the blue cup, most likely, was smashed by mice.