Because Ronan and Hennessy are a mess, cluttered with all kinds of debris inhibiting their abilities. Their mentor guiding them through this learning curve, Bryde, requires them to peel back the insulating layers protecting their inner selves to do this. They _must_ advance to a grand scale of dreaming that is precise and refined, efficiently and effectively utilizing the energy with no waste of effort or outcome and the ley line none the worse for their use. The sloppy, wasteful, 'trial and error' level they're been dreaming at their whole lives that drains the ley line to exhaustion. It's a race against the moderator's persecution as well as the industrial developments that are choking off the essential flow of ley line energy necessary for dreams and dreamers to thrive. Ronan and Hennessy must perfect their skills and abilities in order to help dreams and dreamers everywhere. The fanciful aspects of dreams are there too, but the gravity of their plight remains front and center throughout the story. It's.a spiritual journey and has a lot of depth as a consequence. Not that it doesn't have its hilarious moments (Hennessy's diatribe about Pennsylvania had me in stitches), but on the whole it's about maturing, self exploration and self realization.

It's fair to say Mister Impossible is the most serious book so far. Well, basically, Maggie Stiefvater takes everything you know in the series and turns it on its ear.

Mister impossible paperback