"The Marsh King's Daughter" (Danish: "Dynd-Kongens Datter") is a short fantasy story for children with strong Christian overtones by the Danish author Hans Christian Andersen. It was first published in 1858. It is the second longest of Andersen's stories, after "The Snow Queen".
The title character and protagonist of "The Marsh King's Daughter" is a young woman named Helga. She is the daughter of two supernatural beings, the wicked Marsh King and a fairy princess from Egypt who was captured by the Marsh King. Helga is raised by a Viking and his wife. The Viking's wife soon discovers that Helga is cursed to take two different forms. By day, she is human. By night, she looks like a toad. In her human form, Helga is badly behaved and cruel. In her toad form, she is good-natured. It is only when she begins to feel compassion for someone while in her human form that the spell on Helga is lifted and her mother is freed.
Andersen presents the story as a folktale which storks tell their young.The story is said to have been told for many generations and to have become altered and embellished as a result.
A pair of storks spend the winter in Egypt. In the spring, they fly to Denmark and nest on the chimney of a Viking longhouse. The longhouse is home to a Viking warrior and his wife. Near to the longhouse is a marsh. Beneath it lives the wicked Marsh King. Anyone who steps on the marsh is likely to be dragged underground by the Marsh King, never to be seen again.
One day, father stork sees someone he recognizes as a fairy princess from Egypt. She and two other fairies have put on magical swans' skins in order to fly to Denmark, The fairy princess' father is seriously ill. She has been told that the only thing which can cure him is a flower from the lake in the Danish marsh. When the fairy princess takes off her swan's skin, the other two fairies destroy it. They tell her that she will never return to Egypt and fly away. After they have gone, a tree stump reveals itself to be the Marsh King in disguise. The Marsh King grabs the fairy princess and takes her beneath the lake.
Mother stork is told what has happened to the fairy princess. She is certain that the fairy princess is able to take care of herself and that no harm will come to her. Each day, father stork flies over the lake but sees no sign of the fairy princess. He does, however, see a tall plant begin to grow out of the lake. When the plant's flower opens, father stork sees a tiny baby girl inside it. He realizes that the baby is the daughter of the fairy princess and the Marsh King. He decides to deliver the baby to the Viking's wife, whose husband is away on a raid.
The Viking's wife is delighted to get a daughter, although she soon finds out that the child is very bad tempered. She soon discovers that the child is bewitched. At night, the girl takes on the form of a hideous toad. However, it is only when she takes on the form of a toad that the child becomes well behaved and shows kindness towards her mother. When the Viking returns, he too is delighted to have a daughter. He is pleased that the child is bad tempered and believes that she can grow up to be a warrior. The girl is given the name of Helga. The Viking's wife does not tell her husband that Helga changes shape at night and he never finds out that she does.
In Egypt, the fairy princess' father is still seriously ill. He lies still, neither dead nor truly alive. Father stork finds out that the two other fairies lied to the fairy princess' father. They told him that his daughter was killed by a hunter while in the form of a swan. To punish them, father stork steals their swans' skins and takes them back to Denmark. He keeps them in the hope that he can one day give them to the fairy princess.
Helga grows up to be fierce and cruel. She delights in the animal sacrifices which the Vikings make to their gods. Helga continues to change shape at night. Her body looks something like that of a goblin with a head, arms and legs like those of a toad. It is only in her toad form that Helga vaguely understands love.
The Viking returns from a raid with a Christian priest as one of his prisoners. It is decided that, since he has denied the gods of the Vikings, the priest will be offered as a human sacrifice to those gods. On the evening before he is due to be killed, Helga goes to rescue the priest when she takes on her toad form. The priest is frightened by the sight of the creature at first but realizes that he is being helped by the toad. They ride off together on Helga's horse.
When Helga takes on her human form again at dawn, she immediately tries to kill the priest. However, he is able to overpower her. He fashions a cross from two tree branches tied together with bark. Helga takes the signs that the priest makes and his quotations from the Bible to be evidence that he is a powerful magician and does not try to fight against him anymore. The priest says that he will take Helga to a Christian city where the enchantment on her can be lifted. However, they do not reach their destination because they are attacked by robbers. The robbers kill the priest and the horse. Night is falling when the robbers attack. When Helga changes into a toad, the robbers flee in terror.
Helga in her toad form does not want the priest and the horse to be eaten by wild animals. She tries to dig a grave for them but that proves too difficult. She builds a burial mound for them instead. Constructing the burial mound takes all night. When dawn comes and Helga becomes human again, she still feels some compassion for the dead priest and horse. She climbs up a tree and spends all day there. When evening comes and Helga becomes a toad again, she comes down from the tree and places the cross which the priest made on the burial mound. She traces the wooden cross with her fingers and says the words which she often heard the priest say, "Jesus Christ". The toad's skin then falls off her hands. Helga makes the sign of the cross in the air and she becomes human again.
The dead priest and horse appear before Helga. Now knowing the truth about Helga's origins, the priest tells her that he has to take her back to the lake where she was born. They fly through the air on the horse. At the lake, the priest holds his cross high, swings a censer and sings hymns. Helga joins in with the priest's songs. Helga's mother, still young and beautiful and looking just like Helga, appears. She is sleeping and is being carried along the lake on a carpet of water lilies. The sleeping fairy princess is placed upon the horse.
At dawn, the dead priest and horse disappear but the fairy princess and Helga remain. The two realize that they are mother and daughter. The fairy princess says that she escaped from the Marsh King and spent a long time sleeping beneath the lake. Father stork arrives with the two magical swans' skins. The fairy princess wants to fly to Egypt at once. Helga wants to say goodbye to the Viking's wife, who always treated her kindly, first. Everyone at the Viking longhouse is sleeping. However, in a dream, the Viking's wife sees Helga change from a toad to a kind-hearted woman and then to a swan.
Helga and her mother fly to Egypt with the storks. In Egypt, the fairy princess' father is still lying neither dead nor truly alive. When he sees Helga, he immediately returns to full health. Helga was the flower from the lake in Denmark which the fairy princess was told would cure her father. Helga writes her name on a gold bracelet. She gives it to father stork and tells him to take it to the Viking's wife as a sign that she is still alive. Helga also tells a nightingale to protect the burial mound of the priest and the horse and make sure that birds always sing there.
Years pass. Helga becomes engaged to an Arabian prince. On their wedding night, Helga goes onto the palace's veranda to look at the stars. The stars take on the form of the dead Christian priest. The priest tells Helga that he has come from Heaven, the joys of which are impossible to describe. Helga asks the priest to take her to Heaven for just one minute. The priest reluctantly agrees. He then reluctantly allows Helga to stay for a further two minutes before insisting that it is time for her to go back to the palace. When she comes back, Helga finds that all the wedding guests have gone. Her husband has gone also and soldiers she has never seen before are sleeping in the palace. Helga goes into the garden. She sees that it will soon be dawn and decides that three minutes in Heaven must be equivalent to an entire night on Earth. She sees what she thinks is father stork. She calls out to the bird but he does not recognize her. She tells him that she is Helga from Denmark. The stork says that his great-grandmother told him the story of Princess Helga from Denmark who vanished on her wedding night hundreds of years ago. He adds that there is a monument to the princess in the garden. Helga falls to her knees in front of the monument. As the first beams of the rising sun touch her, her body is changed into a faded flower.