It is a fantastic Ukraine, a fantastic city of Petals. The times are timeless, but stylistically steampunk and the age of steam engines. Eleven-year-old Vira is interested in science, but her mother plans to marry her off just after adulthood. Vira's brother goes to high school. She secretly reads his textbooks and dreams of constructing a portable railroad car in which the petal girls can ride to study at the university.

One day at a fair, a magic key falls into Vira's hands, which the evil sorcerer Clavis seeks. This key is the only way for him to return to his magical world.

Clavis forces Vira to bring the key to an old castle on the edge of town. When Vira opens the door of the castle with the key, she enters a fairy-tale world, where she meets Prince Marcus, who has been locked in the castle by the sorcerer. Vira discovers that Marcus also loves science and does a lot of research in his castle. Clavis, who has flown into the castle with Vira, tries to take the key away from Vira and Marcus. If Clavis has the key, the prince will remain in the castle forever and Vira will not return to her world. Running away from Clavis, Vira and Marcus open one by one seven doors in the castle, and each time they get through it into a new fairy tale.

The population of fairy tale worlds: the Serpent Kozelko, the dragon, the nexie, mermaids, witches, the Iron Nose Woman, the Cossacks - help children to find doors to the real world, and hide them from the evil wizard Clavis, who pursues them to destroy and take possession.

In the finale, Vira and Marcus defeat Clavis using the laws of science. But Vira is badly injured and the key is broken in half. Marcus runs up to Vira, who must be taken to the real world. All the inhabitants of the fairy tale worlds concentrate their energy into one and open the closed door to the real world without the key. Marcus picks Vira up in his arms, steps through the door and enters Vira's room. Carefully he places her on the bed and kisses…

When Vera wakes up, she feels something around her neck, takes it off, looks - it is a half of the key to all doors. The door opens and Vira's parents enter.

Vira holds this half of the key and promises her parents, that she will definitely become an engineer and make a great discovery, which will be a new era for mankind.