I read an ARC copy of this book obtained through First Reads.While I really disliked this book, I can at least recognize that most of what bothered me is a matter of personal opinion. Style choices and plot points that, while I hated them, others would probably like. If you read through my review and think "Why is she whining about that? It sounds fine," then you'd probably like the book. I cannot, in good conscience, call it a bad book, because it's not. But it's not good, either.First of all, there are some things I really like about this book. The zombies, for one. Even though zombies are overplayed these days as the monster, Adams gives them a fun twist and actually plays with it. There's no "Our zombies are different, except we're going to treat them like they're not" in this book. I loved that.The urban fantasy world in this book is delightful. I love the 'magic meets bureaucracy' feel to it, and it's clear Adams put a lot of thought into how her system works. She comes up with some clever stuff. People who have read previous books and liked the setting will not be disappointed.The characters are engaging, the mystery is suitably mysterious, and while I wasn't shocked by the final reveal of the bad guy, I was at least kept properly in the dark until the right time.And then we get to the problems this book has. The writing, frankly, feels very childish to me. Celia's narration reads less like a grown woman, or even a fully-realized and developed character, and more like the blog of a hyper 15 year old girl. There are a lot of phrases and word choices that just seem...juvenile. I had a hard time throughout the book imagining Celia as anything besides very, very young. To be honest, through the first part of the book, I thought it was marketed to teens instead of adults. The pacing in this book is very odd. There's a lot of moving parts in this plot, and they all move in fits and starts. Celia's illness drags on over weeks, and then as soon as it's convenient to the plot, all of a sudden it's an immediate concern that could kill her if it's not fixed right away. Another one of her problems features prominently through the whole book, and at the end is fixed in half a page so that it can be brushed aside in favor of the finale. On the other hand, there are multiple points in the book were seemingly routine things get absurd amounts of detail that grind the narrative to a halt. One section spends three pages on someone feeding Celia while she can't use her hands. Three pages to describe pouring broth in her mouth, an operation that went off without any mishap and then was promptly forgotten. Why was it important enough to get three pages? It wasn't, the pacing is just wonky.The worst pacing problem of them all: The titular Isis Collar doesn't even get a mention until page 330 out of 384, and even then it barely plays a role in the plot. It's a very interesting concept, and it's effects are hinted at throughout the book (by confusing the cast and keeping them from identifying the main bad guy) but they're never really played with or explored. Considering this object is the title of the book, I expected it to have much more of an impact on the plot and/or characters. (And despite the picture on the cover, Celia never wears the thing. She only even touches it once.)And my final problem with this book is Celia herself. She's not an exceptionally poor character. A little bit bland, but that's par for the course when it comes to main protagonists. (Of every gender and every genre; I'm not trying to pick on anyone here.) No, my problem is that she sails through this book unaffected by the events. There's a lot of trauma going on here, some of it personal and some of it cataclysmic, and yet it never trips her up in any way. At most, her physical afflictions bother her, but we're only every told that she's bothered, they don't really affect her actions. At one point she even sees her therapist -- something we're told is a regular event -- and she breaks down crying and spilling out everything that's happened...in a single paragraph of narration. She talks about how she's 'overwhelmed.' "There was so much seething anger, fear, and pain rolling around inside me that I didn't even realize it until it all came out." Except for one problem. This is a first-person narrative. We are literally hearing all of Celia's thoughts throughout the book. Outside of this single line, we don't hear her talk about her 'anger, fear, and pain.' It doesn't affect her. It doesn't bother her. It doesn't slow her down. It doesn't have any impact at all on her ability to function, solve the case, and save the day. There is nothing there for her to overcome. It's just a throwaway line right before they introduce some new problem that will also not affect her in the least. It's a cheap gimmick mean to solicit sympathy that ends up feeling hollow and, by extension, makes Celia feel hollow as well.