Magic, mystery, and mistaken identities are all part of this visually striking fantasy based on a well-known Russian fairy tale. While stopping at a well during a journey, Tsar Yeremey (Mikhail Pugovkin) is confronted by Chudo-Yudo the Lawless (Georgi Millyar), a ill-mannered enchanted creature who lives at the bottom of a lake. Chudo-Yudo refuses to release Yeremey without some sort of tribute, so the Tsar agrees that Chudo-Yudo is allowed to take possession of any of the valuables in his fiefdom that he doesn't know about. However, when Yeremey returns, he learns to his surprise that he has just become a father; terrified that his newborn son will be handed over to Chudo-Yudo, the Tsar makes a secret arrangement with a poor fisherman to exchange babies to keep his child from Chudo-Yudo's clutches. As the children grow to be men, Yeremey pays little attention to pudgy and self-centered Prince Andrei (Sergei Nikolayev), while from a distance he dotes on the strapping fisherman's boy Andrei (Andrei Katyshev); what the Tsar doesn't realize, however, is that there was a mix-up in the exchange of babies, and that his true son has been living with him all along. When Chudo-Yudo decides to claim Prince Andrei as a suitable fiancé for his lovely daughter Barbara (Tatyana Klyuyeva), the sullen young man is spirited away to Chudo-Yudo's underwater lair. Yeremey tells the fisherman's son of what he believes is his true parentage, and the young man sets out to rescue the Prince, little realizing the beauty and charm of Barbara.