I actually really liked this for the most part. It's an appealing mix of genres, part sci-fi, part thriller, but most of all it's horror, as a mass contagion that appears to be spread by sound affects crowds in an interesting and creepy way. There are some genuinely disturbing moments here, and if the characterisation is consistently one-note, then the imagery of the mob, crushing each other and running to death, is certainly compelling. Especially as there seems to be a number of different possible explanations, with the two most likely appearing to be government conspiracy or demons. (Not gonna lie, I was kind of hoping for demons.) And for most of the book, the tension keeps rising and the horror keeps coming, and I was seriously considering giving this four stars and then the end came and it all fell apart for me. The final fifth, perhaps, is the problem. It felt rushed, and the eventual solution to the mystery wasn't that compelling, and - more crucially - didn't seem to fit the tone of the rest of the book.

In short: great idea, fun execution, let down by the ending.