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.