Kristin is kidnapped and killed. While her family grieves, her killer is still at large in the community. Meanwhile Kristen is experiencing the afterlife, and trying to help heal the hearts of her family.
I didn't read "The Lovely Bones" but it seems as though the premise is roughly the same. Kristen's kidnapping and death are experienced from her perspective. She doesn't go into great detail; still, I wouldn't recommend it for younger than 16, probably.
Interesting ideas about the afterlife, obviously not to be taken as doctrine (she doesn't claim that they are, either.)
Overall, not my favorite of hers. I think it was supposed to give families who have lost loved ones in this type of tragedy some hope that the person who died is truly now in a better place, surrounded by love, free from pain, etc., which is fine. Just not one I'll read again.