An advertisement appeared in the Nemukhin newspaper that flying boys were urgently needed for the construction of the Castle in the Air. Petka Vorobyov really wants to take part in this construction, but, unfortunately, he doesn’t know how to fly at all. The lighthouse keeper from the magical land of Letlandia tells Petka that in Nemukhin there lives a flying boy, Lenya Karaskin, who escaped from Letlandia, who can give Petka several lessons in flying skills.