An impolite and arrogant fairy who aggressively pursues Lydia. Bound by the moon spell, which drives away unwanted advances from fairies, Kelpie must bring Lydia the "moon" in order to win her over, although it's clear to everyone but Kelpie she has no interest in him. He follows Lydia all the way to London to bring her back to Scotland. Despite his aggressiveness, Kelpie genuinely loves and cares for Lydia, and comforts her when she's confused (though she protests at times).

His fairy form is that of a black horse, while his human form is that of an attractive young man with dark hair and eyes (his pupils are white swirls). His eyes are able to bewitch both men and women alike, and he has strong magical powers. He has the ability to purify water and cleanse toxins.

"Kelpie" is actually the name of his species, and not his given name (it has not been explicitly mentioned). He and Lydia first met in Scotland. At the time, a middle-aged woman came to Lydia with her tale of a young man whom she was in love with. Lydia discovers that the man is actually a Kelpie; the younger brother of the Kelpie that wants to marry Lydia. After being convinced of their love, Lydia eventually aids the woman and younger Kelpie in their relationship.

Despite first appearances, Kelpie (for the sake of the rest of this article, Kelpie shall refer to the main story's Kelpie) demonstrates considerable concern for Lydia. He has saved Lydia (and inadvertently, Edgar and Co. as well) on several occasions, and has gotten hurt on one occasion in her defense. He recuperates quickly when in water. At least twice, he has tried to protect Lydia by taking her from Edgar's side, as he believes that her being by Edgar is dangerous for Lydia. He is also considerate of Lydia's feelings; rather than blaming her when she broke the spirit of their deal (that she would stay in the fairy world with him if Kelpie would save Edgar), he told her that he would wait till she no longer had anything holding her back in the human world.