Young Prince Vasily, having traveled thousands of miles on his way home, ends up in Trakai Castle, where he shows friendly affection to the Lithuanian Prince Vitovt. The visit turns into a meeting with the beautiful Sophia, the daughter of the owner of the castle, who charms the noble guest at first sight. Despite the obstacles in the form of a rival and the order of the Lithuanian king, who forbids the princess to marry, she does not despair and... fights for her happiness as best she can. But how can they be young if Vasily’s father, Dmitry Donskoy himself, does not approve of their marriage?