The fairy tale is based on two fairy tales by Božena Němcová, "Righteous Bohumil" and "The Black Princess". It tells the story of a weak king and his wife, whose desire for a child leads her to a conspiracy with the devil. The princess, who grows up under the influence of the "impure" powers, only escapes from their power thanks to her love for the fisherman Radek.

The story is based on Czech fairy tales, which depict water sprites as creatures indistinguishable from humans. They can help humans and form deeper relationships with them. A humanized water sprite also helps the fearful Florianek find happiness. However, as it turns out, Florianek would not have won his beloved without his own courage...