(4) Base Camp
Just like Pure, Fuse reads relatively quickly. And—bonus— we're accustomed to the language that the characters use, and we already know the backstory to many of them. So when we start to get information that we learned in Pure, it's more of a oh right moment, rather than a oh wow moment. Yet, we're still giving this a "4" on the tough-o-meter, because there's much more historical and scientific mumbo-jumbo that we need to pay attention to.
But hey, that just makes the book more mysterious, and more exciting to read. We've already gotten past the whole what's a groupie and what were the Detonations malarkey, and now we have to use our noggins to connect the tiny pieces together into a larger puzzle.