Souls are the modus operandi of the books theology. Amon, a mummy, lays it out to Gwen early on in the book. There are over souls and under souls. Ghosts are over souls without a body. Poltergeists are under souls without a body. Brainless zombies are under souls with a body. Vampires are over souls in a body. Were-creatures are the soul of a dead animal trying to inhabit a human. The grampa chimp is an oversoul and undersoul inhabiting a chimp, I think. That crept up later without explanation. It's a very interesting proposition and cosmology that Roberson and Allred created to explain the various beings in the book.
Several things go wrong with the plan. For one, Gwen doesn't remember it. When she comes back she just goes about unliving, working as a gravedigger and living in a tomb with Ellie to keep her company. For another, Xitalu's coming back a lot sooner than Amon had thought. There ends up a rush for Amon to convince Gwen of the need for her training and then the training itself.
All this takes place in Eugene, OR, which is a nice change of locale. I can't think of another story I've read set there. The University of Oregon is a prominent player, too, and the track team even makes an appearance. Spectral attacks at the Prefontaine Classic (it doesn't say it's the classic, but I'm going to pretend it is) are not something I've seen at the annual event. Might make for some record times for those trying to escape.
Three of the four issues where Allred isn't the artist features a back story on one of the characters. In issue 12 it's Ellie. Issue 18 is Diogenes (another Fossor). Kennedy (a zombie/cyborg Dead President, agents of the US government under the command of zombie Abraham Lincoln) is examined in issue 24. Only issue 21 by J. Bone is a standard issue story of what's going on with Gwen and the gangs' travails.
It's something of a maudlin end for Gwen. Not quite happy, not quite sad. Xitalu is defeated with finality, so it's a happy ending for the Earth and its residents.
My only quibble with the story that it seemed to me that the method Gwen used to defeat Xitalu could have been easily discovered by Amon and utilized centuries ago. Perhaps he did know it and chose not to because he wasn't willing to make the sacrifice Gwen made. I suppose I'm taking what Amon says at too much of its surface value, as he proclaimed that his plan was the only way to defeat Xitalu, but he had been shown to be less than candid about other things previously.
In any case, it's well worth buying, whether in singles, trades or, someday, HC.