TOS with an evil mermaid?

[freakizimi7.livejournal.com]

Anyone know this one? TOS McCoy, Spock and Kirk go on shoreleave to a planet with a civilisation that worships the sea. Whil there McCoy tries to heal a woman who's fainted, only to find none of the locals will help him with this other, local woman. Later he finds out she's done something to him and now HE'S drawn to the sea inexplicably and finds himself suddenly able to breathe underwater and haunted by this evil hurt local woman/mermaid beastie thing.

Anyone know where I can find this story again? I stupidly forgot to bookmark it and can't remember how I got to it :(

Thanks for any help anyone can give me.

Freakizimi