To trace the spirit, Eve moves through a bunch of different levels of the afterlife, sometimes alone and sometimes with the help of Kristoff Nash, Savannah's also-dead sorcerer father. While tracking the Nix, Eve also works through her obsession with watching her daughter and also her strange relationship with Kristoff--so in addition to the adventure/horror/supernatural aspect of the story, there's also a dose of romance.
I liked the book, though not as much as the one right before or after it in the series.