His melodies are wonderfully captivating and lovely and the whole charm of German romance lies in them.
The contents of the libretto are:
The gallant Knight, Hugo von Ringstetten has been ordered by the Duke's daughter, Berthalda, to go in search of adventures, accompanied by his attendant Veit. Being detained for three months in a little village cut off from communication with the outer world by an inundation, he sees Undine, the adopted daughter of an old fisherman, named Tobias, and falling in love with her he asks for her hand. In the first act we see the priest uniting the young couple. The Knight recognizes in the old man a traveller, whom he once saved from robbers, and is glad to see him. Undine behaves most childishly and finally says that she has no soul. She is herself grieved, and the others do not believe her. Hugo now tells them of the proud and beautiful Berthalda, whose scarf he received in a tournament, and who sent him away on this adventure. He then returns to the Capital with his young wife, in order to present her at the Ducal court. Meanwhile Veit has met Kühleborn, the mighty King of the water-fairies, and is asked by him, whether his master has quite forgotten Berthalda. The valet gives as his opinion that the poor fisher-maiden is deceived, and will soon be abandoned by her husband. This excites Kühleborn's wrath, for Undine is his daughter, and he forthwith resolves to protect her.
In the second act Undine confesses to her husband, that she is a water-fairy, one of those, whom men call "Undinas". They have no soul, but if they are loved faithfully by man, they are able to gain a soul and through it immortality. Though he shudders inwardly, Undine's purity and loveliness conquer Hugo's fright, and he once more swears to be eternally true to her.
The proud Berthalda, who loves Hugo, has heard with feelings of mingled anger and despair of the knight's marriage. She determines to honor the King of Naples with her hand; but before her wedding takes place, a sealed document has to be opened, which says that Berthalda, instead of being a Duke's daughter, is a poor foundling. Kühleborn, who is present, declares that she is the real child of Undine's fosterparents. Berthalda is now obliged to leave the palace. She loathes her fate and curses her low-born parents. Then Kühleborn derides her and the attendants are about to seize him, in order to turn him out-of-doors, when the statue of the water-god breaks into fragments, while Kühleborn stands in its place, the waters pouring down upon him. All take flight, but Undine raises the prostrate Berthalda, promising her protection in her husband's castle.
In the third act Berthalda succeeds in again drawing Hugo into her nets. Though warned by the waterfairies not to perjure himself, he neglects their advice and Undine finds him in the arms of her rival. He repels his wife, and Kühleborn takes her back into his watery kingdom. But Undine has lost her peace of mind for ever, she cannot forget her husband.
In the fourth act Hugo has given orders to close the well with stones, to prevent all possible communication with the waterfairies. Undine's pale face pursues him everywhere, he continually fancies to hear her soft voice and touching entreaties and to stifle his remorse he appoints the day of his wedding with Berthalda.
His attendant Veit, however, unable to forget his sweet mistress, removes the stones, which cover the well. Undine rises from it and appears at midnight at the wedding. Hugo, forgetting Berthalda, and drawn towards his lovely wife against his will, falls into her arms and dies at her feet. The castle comes crashing down, floods penetrate everywhere, and carry Hugo and Undine into Kühleborn's crystal palace.
Undine obtains pardon for Hugo, and his only punishment is that he must forever stay with his wife in her fairy domains.