Two mischievous siblings, Klotylda and Barnabáš, fail their final exams at the wizardly lyceum. In their father Zachariáš’s absence, they break the strict rule and open the forbidden thirteenth chamber, accidentally freeing the evil sorcerer Vzdoroděj. He enchants all the adults and sets off to find a powerful gemstone that will destroy their father and conquer the realm. Hiding with their stern Aunt Berta, the children must manage the household while improving their magical skills and learning to cooperate. When Berta’s rescue plan falters and Vzdoroděj approaches, Klotylda and Barnabáš face him alone.

At Strašperk Castle, the royal budget is being improved by spooky tours instead of raising taxes. These are directed by the resourceful princess Elvíra. Prince Armin arrives at Strašperk, eager to see a magical creature to prove to his royal father that they really exist. As a little boy, he met a witch in the forest, but his father never believed him. Soon, an unexpected event occurs at Strašperk - during the celebration of the king's birthday, the musicians disappear without a trace, then some servants, and finally the king himself. Panic breaks out in the castle. Elvíra and Armin set out to follow the trail of this mystery. It turns out that things are often not what they seem at first glance. And when it comes to magical creatures, no one knows when the next one will be born.