First of all, a clarification. I was expecting a novel about demon, but this is not the case. Instead, this book is rather the Demon version of the Book Nod. So, after this little surprise, it was still a good book and worth reading. The first and largest part consists of the actual "days of fire" text, written in verses, describing the whole story from the creation of the world until the time of judgement.
The text is often very cryptic, I didn't understand all of it. One needs a lot of background knowledge about the whole world of darkness, not only Demon: the Fallen, but also the other game lines. So you learn also something about vampires, werewolves etc. Still, most of the times I could get an idea, what the text was about. Just to make it clear, this book is not for newbies, but interesting for people who know already a lot about world of darkness.
The second part repeats some selected verses from the first part and shows images matching to the verses. The style of these decent images supports the dark mood of this book, well done.
Finally, the last part tells a frame story about people in the world of darkness investigating about the "days of fire" verses. This section consists of mails, newspaper articles and police reports. Again, well written, however, one word of warning: Some texts are encrypted and although in the end, it is explained how to decode it, you are expected to decode it yourself. This is the most obvious example of how to read this book: You do not simply read it and know then, what it is about, this book expects the reader to puzzle and speculate. If you like this, then it is a good book.