
This is the story of a ghost trying to solve her own murder. She can't remember how she died--did she jump from the balcony, or was she pushed? She tries to recreate the events of the party that led up to her death, going over and over who was in which room, who had the opportunity to kill her, and who had the motive.
That's the basic plot, but there's a lot more going on here. You get Attending Your Own Funeral, Switched At Birth, Accidental Incest, Flying, Ghosts In Love, Afterlife 101, and more delicious tropes. It has sequels, too, but they're not as good as the original.
I still remember my favorite passage. It had to do with Shari's life flashing before her eyes. She sees herself at five years old, with "a spark in her eyes that she'd lose the following year when she entered school." This totally blew my mind in middle school, and it's stayed with me ever since.