The way this story is told is one of the most important aspects of The Demon's Lexicon. Although Sarah Rees Brennan uses a third person voice, we remain close to Nick throughout the book, seeing events unfold through his eyes. And guess what? As incapable of lying as Nick is, he still turns out to be a pretty unreliable narrator.
Why? Because there are crucial pieces of information that he doesn't have (like, say, the fact that he's not human), and therefore his view of each and every event is a little bit skewed. And so, when we get to the big reveal at the end, the part where we—and Nick—figure out what's really going on here, we have to go back through the book and re-evaluate just about everything we thought we knew:
Characters whose motivations we thought we understood appear to us in an entirely new light.
Events we saw in one particular way take on new meaning.
It's a pretty amazing task that Sarah Rees Brennan pulls off here, and it kind of makes our heads spin around for a bit—if you've seen the movie The Sixth Sense, you've encountered this phenomenon before. And if you haven't seen it, well, if you enjoy twists and turns (and aren't easily frightened), we highly recommend it.