Once upon a time, there lived an old man and his wife. Together, they had twelve sons and three daughters. The youngest girl was named Eglė. On a warm summer evening, all three girls decided to go swimming. After bathing with her two sisters, Eglė discovered a serpent in the sleeve of her blouse.
The eldest girl grabbed Eglė's blouse, threw it down, and jumped on it, but the serpent did not leave. Turning to the youngest, Eglė, the serpent spoke to her in a man's voice, saying, "Eglė, promise to become my bride, and I will gladly come out."
In order to get him to leave her clothes, Eglė pledged herself to him, not understanding the possible consequences.
Three days later, thousands of serpents came for Eglė, but her relatives tricked them three times in a row. A goose, a sheep, and a cow were given instead of the girl, despite the warnings of a cuckoo. Finally, the enraged serpents returned and took Eglė with them to their master at the bottom of the sea.
Instead of seeing a serpent, Eglė met her bridegroom Žilvinas, a handsome man and the Serpent Prince. They married and bore four children, living happily.
One day, Eglė wished to visit her home, but her husband would not allow her. In order to be allowed the visit, Eglė would be required to fulfill three impossible tasks: to spin a never-ending tuft of silk, wear down a pair of iron shoes, and bake a pie with no utensils. Upon advice from a sorceress, Eglė was able to complete these tasks. She and her children left Žilvinas to visit her home.
After meeting with Eglė and her children, her family wished to keep her rather than let her return to the sea. They plotted to kill Žilvinas. Eglė's brothers asked her sons to reveal the secret calling of Žilvinas, but they would not. Finally, one of Eglė's daughters disclosed it:
"Žilvinas, dear Žilvinas,
If alive - may the sea foam milk
If dead - may the sea foam blood..."
The twelve brothers then called Žilvinas out from the sea, and killed him with scythes. They kept the secret of their deed from Eglė. Worried, Eglė called her husband, but only foams of blood returned from the sea.
Discovering that her beloved husband was dead, Eglė turned herself and her children into trees. Her sons were turned into strong trees: oak, ash and birch; her daughter was turned into a common aspen, and Eglė was turned into a spruce.
