A trespassing gang of boys encounter a ghost in the ruins of a castle. When they rescue the ghost who is caught in a trapset, they become allies in a fight to prevent ruins from being turned into mushroom farm by the city authorities.

Three friends - Tomás, Hubert and Jozka - are boys growing up in a little town. Tomás lives with his aunt Apolena and uncle Václav. Tomás is a boy with lots of ideas that often end up getting him into trouble not only with his teachers and aunt, but with the other inhabitants of the town as well. He has a crush on his schoolmate Blanka and for her sake he decides to try to get the prize for the best pupil in the school.