A Tsar King finds an injured eagle and nurses it back to health, with the promise of great riches in return. Once recovered, the eagle flies him to three kingdoms in the sky. The first two are owned by the eagle's sisters and their husbands, who each give him an extravagant casket made of iron and silver (chronologically), and the third is owned by the eagle (a Tsar Eagle), his wife, and his mother. There he is given a third, plain casket, but warned never to trade it away as it is priceless.
The Tsar King is given a boat that will return him to his home, but warned not to sleep in it. Inevitably, the Tsar King falls asleep and wakes up on a mysterious island, lost. The Tsar King is visited by the Sea King, who promises to return him home in exchange for one of his caskets. Unwilling to trade one of the first two extravagant caskets, the Tsar King gives him the plain casket. The Sea King claims it contains the soul of a member of the Tsar's kingdom whose home he doesn't know is kept. The Tsar King claims to know every member of his kingdom and every house they live in.
Once he returns to his kingdom, the Tsar King discovers his wife has given birth to a son, and realizes that's whose soul was within the plain casket. He opens the iron casket, which contains a countless number of bulls, cows, horses, rams and sheep, and he opens the silver casket, which contains a splendid garden that appears around his castle, but both pale in comparison to the baby prince's soul.
Years pass and the boy grows into Ivan Tsarevich, who is then sent for by the Sea King. Ivan agrees to go and travels to the Sea King's underwater kingdom. On his way, he sees thirteen white doves that shed their feather dresses and become beautiful maidens. Enchanted by the beauty of the youngest maiden, Vasilisa the Wise, Ivan steals her dress to gain a moment alone with her after her sisters fly away, and Vasilisa reveals the Sea King is her father and angrily waits for him.
Ivan travels to the Sea King's underwater kingdom, where he is tasked with jobs to complete in an impossilbly short amount of time, or be killed. Each time, Ivan only completes the tasks with the help of Vasilisa the Wise. The final task is to pick which one of the Sea King's thirteen daughters he must marry while their faces are covered and they appear identical. With Vasilisa's help, he picks her out all three times, and the two marry.
Ivan Tsarevich soon grows homesick, and he and Vasilisa escape the underwater kingdom, only to be pursued by the Sea King's servants. The couple trick his servants twice using magical disguises, and the third time they are pursued by the Sea King himself. Remembering how his father saved the life of a Tsar Eagle, Ivan calls upon the eagles' aid to escape the Sea King, and they fly away back to Ivan's native kingdom where they have a feast and live happily ever after.