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.

The little mermaid rescues a prince from drowning and falls in love with him. To be with him, she makes a deal with the evil sorceress: her beautiful voice against a life on land. It seems to work at first, the prince is enchanted with her lovely appearance. But the memory of a foreign princess still haunts him: The one who found him on the beach where the mermaid had left him, and whom he (of course) believes to be his saviour. To resolve this mistake is too much for the mute little mermaid, and not even her father, king of all seas, can help her in the impending catastrophe.

On the holidays, ten years old Adam and his little sister Otka, four years junior to him, travel from a village Vykán to their aunt to Prague. Their parents left for Hungary to the world championship in ploughing. The children have the address but they do not know the way to the Northern Town. They set out for a place on foot, across the historical parts of the town.