What happened?
(Spoilers follow, beware)
Hmm.. Well, the characters are troubled teenagers, apparently living on the edge between modern society and a kind of dark fairy-tale world populated by spirits that seem inspired by Eastern European folklore. The narrator has some sort of connection to these spirits, as does the girl Carla. Carla is in an abusive relationship. She sleeps with the narrator, then steals his heart (literally) and hides it. Then, after their friend drowns in an accident, she steals his body and gives it to the witch in the forest. The witch then tells the narrator of Carla having betrayed him and stolen his heart, and that if he betrays her in return to the witch, she'll give him something valuable. He thinks she means the heart, but after he leads Carla to her he discovers its his friend's bones. His friend's ghost is now free, and tells the narrator where the heart is - beyond some sort of fairytale quest zone - but the narrator isn't willing to risk himself to get it (only, it seems, others), and leaves it at that.
That's the plot, but the plot isn't really the important part - it's the juxtaposition of the theme of troubled teenagers with the darkness of the fairytales. The story worked, for me, because of the implicit suggestion that the world of old folklore still exists, outside of the reach of mainsteam society, but it is degraded, and only people in a like state of degradation can connect to it. The kids, being self-destructive and lost, have a connection to something that is equally lost. What made the story great, rather than good, is that it managed to impart all this without explicitly saying it, just by the actions and descriptions by the narrator. The end was great, in a horrific way, because it showed that the supernatural cannot save the narrator - he is too far gone, amoral and uncaring, to ever truly be a hero.