Well, in the book, the mermaid wishes to be human and to walk upon the earth, she makes a deal with the villain, but she can't speak and every step she takes feels like burning daggers. Even after doing all of this for the Prince she wishes to marry, the prince belittles her every chance he gets until finally, he ends up getting set up in a marriage with another woman. The mermaid is heartbroken and dies of grief (and is turned into some kind of sea life, i forgot) and must spend her afterlife in purgatory forever. The story was actually written in the form of a loveletter, as well. The author fell in love with someone who they could not ever be with and wrote the story to express their frustrations and heartbreak.