"Devil" (in contrast to "God," the book featuring the other puppy of this sickening and absolutely disgusting series), is the final installment of Gomorrah's Season One - the fifth entry, and the only one providing some sort of closure to Zoe's story of descent into urban hell, the single character we still recognize throughout all previous books.
Although I wouldn't consider Zoe by any means the star of the series (I don't think there is one with such a large cast), she's one tough cookie, having survived every kind of atrocity possible that can be perpetrated on a woman (not to mention her own infection by the virus!). And here she's finally coming face to face (face to snout?) with Fester, the most awful doggie ever seen in recent horror fiction (at least Cujo had an excuse; Fester, however, grew up to be a psychopath, if there can be psychopaths among dogs).
Fester is going back home to have another taste of his Mother (don't ask!), and he's not only consumed by lust, he's on a rampage! So keep your children safe, lock your men indoors, and guard your women - coz Fester makes no distinctions! He's the real article: a Devil in disguise.