Situation for game-setting, aside from Most Dangerous Game in a dragon's hidden valley-
Your party is in a rural village, in the Svartlund part of the map, all heavy Germanic forests and such. There's an elven circus nearby- not terribly near, but a small troupe occupying space at the local market-faire.
One of the village girls has taken very strange- she moves about in a daze, as if in shock. They found her out by the old oak tree, the sacred/profane/rightly forbidden grove that most folks say belongs to the fairies, out on a night when she ought not to have been. They found her cold and damp and mostly alive, but for the chill. But she's in a deep shock, and won't come out of it. People are afraid of what it means.
Investigation will reveal that the girl (young, pretty, of marrying age but not yet bonded) is alive- she breathes, her blood flows- but she does not respond to much of any stimulus, or rather she's off completely in her own world. She can move, stand if set to it, but does little of her own volition. If you put your ear to her chest- she has no heartbeat.
There are old legends, of fairies and Sidhe nobles stealing away children, or young men and women's hearts. Often there is song involved. The girl was suspected by her parents to be sneaking off to see a sweetheart, and someone heard singing.
There's a young elven man amongst the troupe of entertainers, a rake and a bard, and there's a bit of a charge to lynch him. As he puts it, "If I had the power to pluck out a heart still beating, do you think I'd still be in chains here?!" He swears up and down that the girl had no eyes for him, and he shrugged and moved on a week ago. He's mostly telling the truth. (Possibly he witnessed it, but we'll see)
The legends go, that the girls whose hearts are stolen, sung right out of their breasts, there is rarely a way to save them- they die mad, some crying and screaming and clawing at the doorway to fairyland, while others simply wander aimlessly and fade away, heartless, soulless, cut-stringed dolls. But, this being loosely fairytale-based, there could very well be a quest to save her life, by going in and retrieving her heart from the unscrupulous demigod who's stolen it.
I'm not sure of the particulars, but I know the image I have for it is that the being that stole the girl's heart and ate it/absorbed it, didn't know what he was getting into. He got in too deep, maybe something about stealing the heart of a mortal in the wrong way makes you mortal, or capable of love in a nature alien to it, and either way it's making him sick. In the night, through the trees, you see this dark rider on a terrifying steed, trotting through the glen- the rider's slumped, then falls completely over, and I dunno, there's something about big bad dudes being undone by underestimating true love that appeals to me, whether or not it's love they're actually involved in.
Must hammer this into an adventure for gamers.